ENIGMA is a free game and application development toolkit, utilizing GCC and a series of parsers to convert a high level, script-like language based on Game Maker's GML, into C++. The toolkit employs a mixture of both C++ and GML, accepting either.
Lixoo is a extensible, fast and small 2D point'n'click adventure game engine. It features the engine itself and an IDE that let you create full-featured games just by writing the essential code of the game.
JFrog is a free distributed components-oriented framework created to develop multiplatform game engines with high source code reusability. Its possible to create game engines for personal computers and handhelds. Before this project was Amphibian.