BYOND - BYOND is the premier community for making and playing online multiplayer games.
pixeldudesmaker - Simple, web-based pixel art character generator.
ct.js - ct.js is a 2D game editor (desktop app) based on web technologies.
Game Character Hub - helper program for game design (RPG Maker XP/VX and more)
Godot Engine - Feature-packed 2D and 3D open source game engine.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.