OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
Godot Engine - Feature-packed 2D and 3D open source game engine.
Synfig Studio - Just another WordPress site
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
BYOND - BYOND is the premier community for making and playing online multiplayer games.