Bitsy : Bitsy is a little editor for little games or worlds. The goal is to make it easy to make games where you can walk around and talk to people and be som...
Crafty : JavaScript Game Engine, HTML5 Game Engine
InK - Interface Kit : Ink is a set of tools for quick development of web interfaces.
LÖVE is a framework for making 2D games in the Lua programming language. LÖVE is totally free, and can be used in anything from friendly open-source hobby projects, to evil, closed-source commercial ones.