Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Unity - The multiplatform game creation tools for everyone.
PICO-8 - Lua-based fantasy console for making and playing tiny, computer games and programs.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Pixelorama - Free and open source sprite editor and animator, ideal for pixel art.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.