norman001 {l Wrote}:What is the best open source game engine?
There isn't a "best" open source game engine.
Godot is the closest to Unity. It does 2D and 3D. It has a nice UI and has stores with content for it. Godot 3 is the well tested version but Godot 4 was recently released and has improved 3D capabilities.
Love2D uses lua for the programming language and is fairly simple to get started.
Ogre3d and various other 3D engines exist but I have no experience with them. There are also various game engines or frameworks for 2D. Since you haven't said anything about your needs it is hard to advise on possible choices.
You also never answered "What can you contribute yourself?". Are you a programmer and intend to develop the game? Are you just the game designer and need programmers, artists, etc. to get this done? Open source developers tend not to contribute to a project that hasn't shown some viability. You will need to bring the game forward enough to prove viability. That doesn't mean you need good graphics but you need something. Maybe you could get people on board with a good design doc or paper prototype but I can't think of any example of that in the past.