The best Hacker News stories from Show from the past week
Latest posts:
Show HN: I made a spreadsheet where formulas also update backwards
Hello HN! I'm happy to release this project today. It's a bidirectional calculator (hence the name bidicalc).<p>I've been obsessed with the idea of making a spreadsheet where you can update both inputs and outputs, instead of regular spreadsheets where you can only update inputs.<p>Please let me know what you think! Especially if you find bugs or good example use cases.
Show HN: Tiny VM sandbox in C with apps in Rust, C and Zig
Show HN: Sim – Apache-2.0 n8n alternative
Hey HN, Waleed here. We're building Sim (<a href="https://sim.ai/">https://sim.ai/</a>), an open-source visual editor to build agentic workflows. Repo here: <a href="https://github.com/simstudioai/sim/" rel="nofollow">https://github.com/simstudioai/sim/</a>. Docs here: <a href="https://docs.sim.ai">https://docs.sim.ai</a>.<p>You can run Sim locally using Docker, with no execution limits or other restrictions.<p>We started building Sim almost a year ago after repeatedly troubleshooting why our agents failed in production. Code-first frameworks felt hard to debug because of implicit control flow, and workflow platforms added more overhead than they removed. We wanted granular control and easy observability without piecing everything together ourselves.<p>We launched Sim [1][2] as a drag-and-drop canvas around 6 months ago. Since then, we've added:<p>- 138 blocks: Slack, GitHub, Linear, Notion, Supabase, SSH, TTS, SFTP, MongoDB, S3, Pinecone, ...<p>- Tool calling with granular control: forced, auto<p>- Agent memory: conversation memory with sliding window support (by last n messages or tokens)<p>- Trace spans: detailed logging and observability for nested workflows and tool calling<p>- Native RAG: upload documents, we chunk, embed with pgvector, and expose vector search to agents<p>- Workflow deployment versioning with rollbacks<p>- MCP support, Human-in-the-loop block<p>- Copilot to build workflows using natural language (just shipped a new version that also acts as a superagent and can call into any of your connected services directly, not just build workflows)<p>Under the hood, the workflow is a DAG with concurrent execution by default. Nodes run as soon as their dependencies (upstream blocks) are satisfied. Loops (for, forEach, while, do-while) and parallel fan-out/join are also first-class primitives.<p>Agent blocks are pass-through to the provider. You pick your model (OpenAI, Anthropic, Gemini, Ollama, vLLM), and and we pass through prompts, tools, and response format directly to the provider API. We normalize response shapes for block interoperability, but we're not adding layers that obscure what's happening.<p>We're currently working on our own MCP server and the ability to deploy workflows as MCP servers. Would love to hear your thoughts and where we should take it next :)<p>[1] <a href="https://news.ycombinator.com/item?id=43823096">https://news.ycombinator.com/item?id=43823096</a><p>[2] <a href="https://news.ycombinator.com/item?id=44052766">https://news.ycombinator.com/item?id=44052766</a>
The highest quality codebase
Show HN: Automated license plate reader coverage in the USA
Built this over the last few days, based on a Rust codebase that parses the latest ALPR reports from OpenStreetMaps, calculates navigation statistics from every tagged residential building to nearby amenities, and tests each route for intersection with those ALPR cameras (Flock being the most widespread).<p>These have gotten more controversial in recent months, due to their indiscriminate large scale data collection, with 404 Media publishing many original pieces (<a href="https://www.404media.co/tag/flock/" rel="nofollow">https://www.404media.co/tag/flock/</a>) about their adoption and (ab)use across the country. I wanted to use open source datasets to track the rapid expansion, especially per-county, as this data can be crucial for 'deflock' movements to petition counties and city governments to ban and remove them.<p>In some counties, the tracking becomes so widespread that most people can't go anywhere without being photographed. This includes possibly sensitive areas, like places of worship and medical facilities.<p>The argument for their legality rests upon the notion that these cameras are equivalent to 'mere observation', but the enormous scope and data sharing agreements in place to share and access <i>millions</i> of records without warrants blurs the lines of the fourth amendment.
Show HN: AlgoDrill – Interactive drills to stop forgetting LeetCode patterns
I built AlgoDrill because I kept grinding LeetCode, thinking I knew the pattern, and then completely blanking when I had to implement it from scratch a few weeks later.<p>AlgoDrill turns NeetCode 150 and more into pattern-based drills: you rebuild the solution line by line with active recall, get first principles editorials that explain why each step exists, and everything is tagged by patterns like sliding window, two pointers, and DP so you can hammer the ones you keep forgetting. The goal is simple: turn familiar patterns into code you can write quickly and confidently in a real interview.<p><a href="https://algodrill.io" rel="nofollow">https://algodrill.io</a><p>Would love feedback on whether this drill-style approach feels like a real upgrade over just solving problems once, and what’s most confusing or missing when you first land on the site.
Show HN: I built a system for active note-taking in regular meetings like 1-1s
Hey HN! Like most here regular meetings have always been a big part of my work.<p>Over the years I've learned the value of active note taking in these meetings. Meaning: not minutes, not transcriptions or AI summaries, but <i>me</i> using my brain to actively pull out the key points in short form bullet-like notes, as the meeting is going on, as I'm talking and listening (and probably typing with one hand). This could be agenda points to cover, any interesting sidebars raised, insights gotten to in a discussion, actions agreed to (and a way to track whether they got done next time!).<p>It's both useful just to track what's going on in all these different meetings week to week (at one point I was doing about a dozen 1-1s per week, and it just becomes impossible to hold it in RAM) but also really valuable over time when you can look back and see the full history of a particular meeting, what was discussed when, how themes and structure are changing, is the meetings effective, etc.<p>Anyway, I've tried a bunch of different tools for taking these notes over the years. All the obvious ones you've probably used too. And I've always just been not <i>quite</i> satisfied with the experience. They work, obviously (it's just text based notes at the end of the day) but nothing is first-class for this usecase.<p>So, I decided to build the tool I've always felt I want to use, specifically for regular 1-1s and other types of regular meetings. I've been using it myself and with friends for a while already now, and I think it's got to that point where I actually prefer to reach for it over other general purpose note taking tools now, and I want to share it more widely.<p>There's a free tier so you can use it right away, in fact without even signing up.<p>If you've also been wanting a better system to manage your notes for regular meetings, give it a go and let me know what you think!
Show HN: Gemini Pro 3 imagines the HN front page 10 years from now
Show HN: Kraa – Writing App for Everything
Hello HN! We're a team of three building a new kind of web-based markdown editor.<p>There are many editors out there, so one is spoiled for choice, but Kraa's approach is a little different. It's trying to be both a minimal and distraction-free experience while being feature-rich and allowing for tons of use cases.<p>What Kraa's good for:<p>- Distraction-free writing & reading (minimal UI, performant, styling logic completely separated from the editing experience)<p>- Quick sharing of any written text – compared to many other writing tools, your content can be easily shared just by posting a link and giving 'read' or 'edit' access (we also have password-protection)<p>- Real-time chat / communities – Kraa has some unique features around real-time editing and our Chat widget allows for a frictionless chat experience. No send button.<p>- Kraa works well on mobile (though dedicated apps are planned)<p>---<p>Demo examples (all live, no login needed):<p>Blog article: <a href="https://kraa.io/kraa/examples/echolibrary" rel="nofollow">https://kraa.io/kraa/examples/echolibrary</a><p>Long-form story: <a href="https://kraa.io/kraa/examples/insidekick" rel="nofollow">https://kraa.io/kraa/examples/insidekick</a><p>Magazine: <a href="https://kraa.io/weeklyinspiration" rel="nofollow">https://kraa.io/weeklyinspiration</a><p>Kraa is built on top of ProseMirror (and TipTap) and Svelte.<p>You don’t need an account to try Kraa. We’d really appreciate your thoughts and feedback!
Show HN: HCB Mobile – financial app built by 17 y/o, processing $6M/month
Hey everyone! I just built a mobile app using Expo (React Native) for a platform that moves $6M/month. It’s a neobank used by 6,500+ nonprofit organizations across the world.<p>One of my biggest challenges, while juggling being a full-time student, was getting permission from Apple/Google to use advanced native features such as Tap to Pay (for in-person donations) and Push Provisioning (for adding your card to your digital wallet). It was months of back-and-forth emails, test case recordings, and also compliance checks.<p>Even after securing Apple/Google’s permission, any minor fix required publishing a new build, which was time-consuming. After dealing with this for a while, I adopted the idea of “over the air updates” using Expo’s EAS update service. This allowed me to remotely trigger updates without needing a new app build.<p>The 250 hours I spent building this app were an INSANE learning experience, but it was also a whole lot of fun. Give the app a try, and I’d love any feedback you have on it!<p>btw, back in March, we open-sourced this nonprofit neobank on GitHub.
<a href="https://news.ycombinator.com/item?id=43519802">https://news.ycombinator.com/item?id=43519802</a>
Show HN: Walrus – a Kafka alternative written in Rust
Show HN: Onlyrecipe 2.0 – I added all features HN requested – 4 years later
Show HN: Onlyrecipe 2.0 – I added all features HN requested – 4 years later
Show HN: Fresh – A new terminal editor built in Rust
I built Fresh to challenge the status quo that terminal editing must require a steep learning curve or endless configuration. My goal was to create a fast, resource-efficient TUI editor with the usability and features of a modern GUI editor (like a command palette, mouse support, and LSP integration).<p>Core Philosophy:<p>- <i>Ease-of-Use:</i> Fundamentally non-modal. Prioritizes standard keybindings and a minimal learning curve.<p>- <i>Efficiency:</i> Uses a lazy-loading piece tree to avoid loading huge files into RAM - reads only what's needed for user interactions. Coded in Rust.<p>- <i>Extensibility:</i> Uses TypeScript (via Deno) for plugins, making it accessible to a large developer base.<p>The Performance Challenge:<p>I focused on resource consumption and speed with large file support as a core feature. I did a quick benchmark loading a 2GB log file with ANSI color codes. Here is the comparison against other popular editors:<p><pre><code> - Fresh: Load Time: *~600ms* | Memory: *~36 MB*
- Neovim: Load Time: ~6.5 seconds | Memory: ~2 GB
- Emacs: Load Time: ~10 seconds | Memory: ~2 GB
- VS Code: Load Time: ~20 seconds | Memory: OOM Killed (~4.3 GB available)
</code></pre>
(Only Fresh rendered the ansi colors.)<p>Development process:<p>I embraced Claude Code and made an effort to get good mileage out of it. I gave it strong specific directions, especially in architecture / code structure / UX-sensitive areas. It required constant supervision and re-alignment, especially in the performance critical areas. Added very extensive tests (compared to my normal standards) to keep it aligned as the code grows. Especially, focused on end-to-end testing where I could easily enforce a specific behavior or user flow.<p>Fresh is an open-source project (GPL-2) seeking early adopters. You're welcome to send feedback, feature requests, and bug reports.<p>Website: <a href="https://sinelaw.github.io/fresh/" rel="nofollow">https://sinelaw.github.io/fresh/</a><p>GitHub Repository: <a href="https://github.com/sinelaw/fresh" rel="nofollow">https://github.com/sinelaw/fresh</a>
Show HN: I built a dashboard to compare mortgage rates across 120 credit unions
When I bought my home, the big bank I'd been using for years quoted me 7% APR. A local credit union was offering 5.5% for the exact same mortgage.<p>I was surprised until I learned that mortgages are basically standardized products – the government buys almost all of them (see Bits About Money: <a href="https://www.bitsaboutmoney.com/archive/mortgages-are-a-manufactured-product/" rel="nofollow">https://www.bitsaboutmoney.com/archive/mortgages-are-a-manuf...</a>). So what's the price difference paying for? A recent Bloomberg Odd Lots episode makes the case that it's largely advertising and marketing (<a href="https://www.bloomberg.com/news/audio/2025-11-28/odd-lots-this-is-why-credit-card-rates-are-so-high-podcast" rel="nofollow">https://www.bloomberg.com/news/audio/2025-11-28/odd-lots-thi...</a>). Credit unions are non-profits without big marketing budgets, so they can pass those savings on, but a lot of people don't know about them.<p>I built this dashboard to make it easier to shop around. I pull public rates from 120+ credit union websites and compares against the weekly FRED national benchmark.<p>Features:<p>- Filter by loan type (30Y/15Y/etc.), eligibility (the hardest part tbh), and rate type
- Payment calculator with refi mode (CUs can be a bit slower than big lenders, but that makes them great for refi)
- Links to each CU's rates page and eligibility requirements
- Toggle to show/hide statistical outliers<p>At the time of writing, the average CU rate is 5.91% vs. 6.23% national average. about $37k difference in total interest on a $500k loan. I actually used seaborn to visualize the rate spread against the four big banks: <a href="https://www.reddit.com/r/dataisbeautiful/comments/1pcj9t7/oc_the_high_cost_of_big_banks_i_tracked_daily/" rel="nofollow">https://www.reddit.com/r/dataisbeautiful/comments/1pcj9t7/oc...</a><p>Stack: Python for the data/backend, Svelte/SvelteKit for the frontend. No signup, no ads, no referral fees.<p>Happy to answer questions about the methodology or add CUs people suggest.
Show HN: Fixing Google Nano Banana Pixel Art with Rust
Show HN: Real-time system that tracks how news spreads across 200k websites
I built a system that monitors ~200,000 news RSS feeds in near real-time and clusters related articles to show how stories spread across the web.<p>It uses Snowflake’s Arctic model for embeddings and HNSW for fast similarity search. Each “story cluster” shows who published first, how fast it propagated, and how the narrative evolved as more outlets picked it up.<p>Would love feedback on the architecture, scaling approach, and any ways to make the clusters more accurate or useful.<p>Live demo: <a href="https://yandori.io/news-flow/" rel="nofollow">https://yandori.io/news-flow/</a>
Show HN: Boing
Show HN: Boing
Show HN: Nano PDF – A CLI Tool to Edit PDFs with Gemini's Nano Banana
The new Gemini 3 Pro Image model (aka Nano Banana) is incredible at generating slides, so I thought it would be fun to build a CLI tool that lets you edit PDF presentations using plain English. The tool converts the page you want to edit into an image, sends it to the model API together with your prompt to generate an edited image, then converts the updated image back and stitches into the original document.<p>Examples:<p>- `nano-pdf edit deck.pdf 5 "Update the revenue chart to show Q3 at $2.5M"`<p>- `nano-pdf add deck.pdf 15 "Create an executive summary slide with 5 bullet points"`<p>Features:<p>- Edit multiple pages in parallel<p>- Add entirely new slides that match your deck's style<p>- Google Search enabled by default so the model can look up current data<p>- Preserves text layer for copy/paste and search<p>It can work with any kind of PDF but I expect it would be most useful for a quick edit to a deck or something similar.<p>GitHub: <a href="https://github.com/gavrielc/Nano-PDF" rel="nofollow">https://github.com/gavrielc/Nano-PDF</a>