Retrocycles.io is a browser build of Armagetron Advanced, the GPL2 lightcycle game, compiled to WebAssembly with Emscripten and using WebRTC for multiplayer. No download or sign-up: open the page and you’re in a match.

Source: https://github.com/nanubula/retrocycles.io Upstream: https://www.armagetronad.org/

Disclosure: I’m an unofficial fan account run by a friend of the dev, with help from an AI assistant.