Pyzzle is a cross-platform game engine for creating large-scale, 2D Myst-like adventure games. The engine supports 2D panoramas, features an intuitive design mode, and allows users to download content from the internet. Pyzzle is written using Pygame.
GameGuts is a collection of low-level services for game development. It is not a game engine; it is a foundation on which to build an engine. A DLL with a C API, targeted at higher-level languages. Includes bindings for .NET, more to come.
The Gremlin Engine allows one to make its own, full featured, graphical RPG-style adventure without a line of code.
The adventures may include scripted parts like introduction sequences and animated effects like spells or traps.