There are two different applications here, Mapcraft and WorldGen. The former is for hand crafting maps of a single world or small area, the latter is for an automated production line generation of thousands of worlds in a short period of time.
The maps generated by both are incompatible with each other, and serve completely different purposes.
MapCraft is a Java Swing application and the binaries for this can be downloaded from the sourceforge website. Installation notes are available in the download.
This is not yet in a state designed for public release, but if you know what you're doing, or just want to look at the code, it can be downloaded from the subversion repository.
It is a server-side product with a Web front end (tested in Tomcat). However, a lot of the functionality is currently only available from the command line.