writes "HubbleSite has a fascinating module where you can learn all you wanted to about black holes, including a module to try and create one from various sizes relative to the Sun."Link to Original Source
writes "basiCommunication is a new open source software package designed for businesses, universities, and other organizations that wish to set up their own discussion network. Final exams are fast approaching, and this would be great for studying in groups as anyone can set up a server to host study sessions on the network. It features instant messaging, moderated rooms, virtual chalkboards, file sharing, among other things. It also works with both Windows and Macintosh clients!"