The Internet BBS is a simple evolution of the Dialup BBS that flourished in the 80's. Internet BBS's were (and still are) virtual communities allowing users to chat and leave messages. Some even allow the old door games to be played.
Source for the major BBSs can be found online.
See also: ISCA BBS, Soncrest BBS, Jungle BBS, Eagles Nest, YAWC, Citadel, Wildcat, Pirates (among others).