We're working on a game engine in Zig[0]
If you're looking for interesting Zig codebases to read, you might be interested in our low-level audio input/output library[1] or our module system[2] codebase - the latter includes an entity component system and uses Zig's comptime to a great degree to enable some interesting flexibility (dependency injection, global view of the world, etc.) while maintaining a great amount of type safety in an otherwise dynamic system.