Recs.
Updated
Godot is a free, open-source, and MIT licensed game development environment for 2D and 3D games.
SpecsUpdate
Pros
Pro Friendly towards Version Control Systems
The engine is build not only to support version control but to really use it. Scene files for example which usually get compiled into some sort of unreadable data stay in a text format - that way you can actually see your changes in a version control system like Git.
Pro Under constant development
This engine barely released one year ago has more than 1000 forks on github and about 100 developers. Not only that just a bit of browsing trough issues you will quickly find out the dev community loves new esp free technology and does not shy away from completely rewriting parts of the engine. The audio engine is being completely rewritten to use threads and so forth.
Cons
Con Primarily supports own proprietary language (GD Script)
While it's very accessible, and if you know Python you'll pick it up fast, having to learn a new language to fully make use of the platform can be a bit discouraging. And for those learning to code as well as learning Godot for the first time, many would rather learn a language they can 'take with them' when they explore other platforms in the future.