Pair programming returns, CAD gets MCP, and models play StarCraft

Welcome back to Builders Feed. Every day: what real builders shipped, why it matters, and what you could build next.

Shipped

1. Petal: open-source pair programming, ScreenHero-style

Four people from the original CoScreen team rebuilt multi-cursor, low-latency pair programming as a free, open-source tool after Datadog sunset CoScreen. 220+ points on Show HN.
Why it matters: Screen sharing shows a partner's screen; Petal-style pairing lets both people actually click and type. Open-sourcing it keeps a beloved workflow from dying with an acquisition.
petal.live · HN discussion

2. Guitoro: a virtual guitar you strum with your keyboard

A free browser guitar using recordings of real instruments — strum with keyboard, mouse, or touchscreen, pick acoustic, classical, electric, or bass, and slow songs to 20% to practice. 560+ points on Show HN.
Why it matters: No signup, no download, no instrument required. It's a reminder that a polished, instant-on web app can still out-delight a native install.
guitoro.com · HN discussion

3. Unfenced: land for sale that borders public land

A listing site filtered to one niche: parcels for sale that border public land. 310+ points on Show HN.
Why it matters: The data was always public — the product is the join. Vertical search built on one sharp filter can beat a generic listings giant for the buyers who care about that filter.
unfenced.land · HN discussion

4. StarSkirmish Bench: LLMs play StarCraft by writing code

A refreshed benchmark where flagship models from OpenAI, Anthropic, Google, and others play StarCraft: Brood War not by clicking, but by writing code. 190+ points on Show HN.
Why it matters: Games force long-horizon strategy, resource trade-offs, and recovery from mistakes — things single-turn chat benchmarks barely touch. Code-as-controller makes every decision inspectable.
starskirmish.com/bench/v0-2 · HN discussion

5. SolidCraft: open-source parametric CAD in Rust, with MCP support

An open-source parametric 3D CAD application built in Rust, for desktop and web, with automation through MCP. 140+ points on Show HN.
Why it matters: MCP support means agents can drive a real CAD model, not just chat about one. Design tools that agents can operate are becoming design tools agents can build in.
github.com/bherbruck/solidcraft · HN discussion

6. Flipflop: persistent tunnels for file sharing, powered by Iroh

Filesharing built to leave always-on, trusted channels between your devices and people — born from frustration with one-off transfer tools. Built in Rust.
Why it matters: Most file tools optimize a single send. A persistent, trusted tunnel optimizes the relationship — the tenth transfer to the same person should take zero setup.
github.com/andunieee/flipflop · HN discussion

7. Parsimony: a benchmark for how much code AI models add

An open-source benchmark that takes patches from DeepSWE, SWE-bench Verified, and SWE-bench Live and counts net "coding units" — statements, calls, and literals — instead of raw lines, so cramming isn't rewarded.
Why it matters: Solve rate alone rewards bloated patches that humans later have to maintain. Measuring how much code a model adds is measuring the maintenance bill it leaves behind.
parsimony.lasu.dev · HN discussion

Build this

Idea 1: One-filter vertical search for everything

Unfenced is one public dataset joined to listings with one sharp filter. Re-run that playbook: homes within a 10-minute walk of a trailhead, rentals with verified gigabit fiber, or commercial space near freight rail. Pick a filter a specific buyer obsesses over, join two public datasets nobody has joined, and charge for saved searches and alerts.

Idea 2: A bloat report for every agent pull request

Parsimony scores models; StarSkirmish scores strategy. Bring both to CI: a bot that comments on every coding-agent PR with tests passed, net coding units added, and files touched, then rolls it into a weekly leaderboard per agent and per repo. Teams already track agent cost — almost nobody tracks agent bloat. Be the tool that does.

Builders Feed is curated daily. Got something you shipped? Reply or tag @buildersfeed on X.