https://hypersomnia.xyz/

An online shooter with ridiculously fast dynamics. Challenge your friend to an intense duel, or gather two clans to fight a spectacular war.

From the source code page:

Hypersomnia is a competitive arena released as free software.

It brings together:

 - The tactics of Counter-Strike,
- The dynamics of Hotline Miami,
- The pixel art nostalgia of oldschool RPGs..
- ..and the potential for limitless community content thanks to an in-game map editor!

The game is already playable and runs a server instance 24/7.