The Asylum game and the Dagon engine were developed by the Senscape indie game studio. An SDK is also being developed to allow for gamers to more easily develop mods to the Asylum game.
Dagon is modular and cross-platform with current support for Linux, Mac OS X, and Windows. Dagon uses Lua for scripting, OpenGL graphics rendering, FreeType for font handling, OpenAL for audio, Theora for video, and Ogg Vorbis for audio.
The code to the Dagon Adventure Game Engine can be found hosted on GitHub.
Details on Asylum can be learned at Senscape.net. Embedded below is also a video about Asylum, which was conceived as a Kickstarter project.