A game dev jam to create a winter-themed open source game was community-initiated at the Godot forums. The (vote-determined) winner will get a budget of USD 50 to have donated to an open source project of their choice.
What is Godot?
Godot is a game engine. No wait, it's actually a game development IDE with its own Lua-based scripting language.
As far as I can tell, it's a promising project that is a bit buggy, especially when it comes to mobile exports. It has some UI flaws (subjectivity warning) but still, open source Godot is more appealing than proprietary Unity 3D.
If you want to try making a game in Godot, I recommend this official tutorial as a starting point. Good luck & great success to you!
Another way to support Godot: "like" it as a Unity 3D alternative on alternativeTo.