Funkin

Scalable open-source game backend server: multiplayer, matchmaking, leaderboards, chat, and social features for games.

A Flutter based game engine.

shapez is an open source base building game on Steam inspired by factorio!

Terasology - open source voxel world

Esoterica Engine

A game engine made as part of the Kohi Game Engine series on YouTube (and Twitch!), where we make a game engine from the ground up using C and Vulkan.