Twine - Twine is an open-source tool for telling interactive, nonlinear stories.
Blitz3D - Create 2D and 3D Games for Windows.
RenPy - Ren'Py is a free and cross-platform visual novel engine that helps you use words, pictures, and...
BlitzPlus - Create 2D Games for Windows.
Quest - Quest lets you create sophisticated text-based games, without having to program.
Monkey 2 - An easy to use, cross platform, games oriented programming language