AlanIDE, the complete Alan Integrated Development Environment, is an experimental (although still quite useful) application build on top of Eclipse. Here you can download AlanIDE as a complete application for your system. You will need an Alan compiler to actually compile the Alan source into a game and an interpreter to run it. You can find them here.
Read more about AlanIDE here.
Note that you need a recent Java runtime to run AlanIDE.