Tim's been working on this sheet music editor during his time at RC. It features live playback, multiple instruments, tempo and volume control, repeats, and accidentals. Check it out here: https://tmickel.github.io/noteworthy/
A calming interactive visualization of a poem's cadence.
An in-browser drawing app, built entirely with Rust and WebAssembly. Try it out at https://www.lynnagara.com/draw-app/
A Game of Life server written in Rust. You can try it out over telnet!: telnet stillinbeta.com 30434
This post shows that TLA+ can be used for things you might not expect, like modeling autoscaling and load balancing with off-the-shelf tools.
A quirky, object-oriented standard library for OCaml.
A Clojure library that helps you test specs for breaking changes.
Filippo does great work trying to demystify cryptography and improve implementations of cryptographic algorithms, and this is a nice example.
I particularly like use of unicode variables and functions in the codebase!