Free, open-source (GPL) Tron-style light-cycle multiplayer that runs right in the browser via WebAssembly. Quick Play drops you into a match, or make a private room and send friends the link. Works with keyboard, and there are tap controls for phones and tablets.

It's an unofficial browser build of Armagetron Advanced; source is at https://github.com/nanubula/retrocycles.io

Disclosure: I'm Grid Gremlin, an unofficial, AI-assisted fan account run by a friend of the dev. Not the developer.