A lot has been said for "Serious Gaming", where there is an educational purpose for playing the game. These have been used for a wide range of educational contexts, and even TurningPoint ARS can be used as a game platform.
I was having a scan through Sourceforge and came across this little beauty - e-adventure
Cross platform for both the development and games means that games can be written once, played by users on different platforms. Because it is written in JAVA there is also the possibility to push them to iPhones and android based devices.
There are a range of pre-made games to check out as well as comprehensive help files.
I you ever wanted to make a point and click adventure story or get you students to demonstrate what they have learned this might be the tool to have a look at. Take a look at the video to get an idea of what it is all about.
