Open Source on Springrts engine. Zero-K is a traditional real time strategy game with a focus on player creativity through terrain manipulation, physics, and a large roster of unique units - all while being balanced to support competitive play.
Factorio-like tower defense game. Build production chains to gather more resources, and build complex facilities.
Ad-less chess server powering lichess.org, with official iOS and Android client apps.
Voxel game engine (formerly Minetest). Play one of our many games, mod a game to your liking, make your own game, or play on a multiplayer server.
Minimalist text adventure game for your browser.
Transport tycoon simulation game.
The Battle for Wesnoth is an Open Source, turn-based tactical strategy game with a high fantasy theme, featuring both singleplayer and online/hotseat multiplayer combat.