uPortal appears to be a servlet application that will run in any compliant servlet containter. As far as reading the source in one evening, that might have been true for the first version, but the second version appears to have grown significantly. There are 260 .java files, and I think you would be in for a very long evening if you planned to read all of the source in one sitting.
I downloaded their quick-start application (includes tomcat, ant, and a Hypersonic SQL db). The application was easy to setup and start, but it threw an execption when I went to the start page, so I couldn't really get a good feel for what it was about.
