Some things I've created, maintain or participate in in some fashion:
Declarative testing of HTTP APIs.
The canonical HTTP API for tiddlers: small chunks of content on the web.
A flexible wiki and application platform built on TiddlyWeb.
A wiki implementing Purple Numbers for granular addressability and transclusion. Long dead but the foundation on which a concept known as PurpleUniverse was built: 15 years later still the best collaborative environment I've ever worked with.
I'm "core" in a few projects in OpenStack: open source software for creating and managing cloud infrastructure and services.
Test WSGI applications with real http clients without a server.