From The BBS Corner:
Bulletin Board Systems (BBS) are basically self-contained online communities. A BBS is almost like a miniturized Internet. A BBS has a variety of things for users to do - Read and Write messages in Discussion Forums, Upload and Download files, and Play online games. If you're familiar with the concept of Facebook - it's very similar, just on a smaller scale.
Kangaroo Punch mainly focuses on retro software or new software for retro machines. What better way to have a presence online than with a retro BBS?