Spring Engine
An open 3D RTS engine with large maps, unit simulation, network synchronization, and Lua game logic.
Why use it
Its specialization avoids rebuilding lockstep, pathfinding, and mass-unit tools in a general engine.
Where it fits
Find engines, frameworks, code libraries, version control, and production automation.
What to check
The architecture is RTS-centric; content production and shipping still depend on a concrete game framework and community tools.