A BBS in the style of Compuserve. Simpler than the others, it enjoyed its heyday in the early 1990s, before the Internet and WWW took off.
As of October 1999, Genie is still around, having changed owners (from General Electric to Yovelle/IDT). It has made some half-hearted attempts to move to the web, none of any note. Mainframe based, it will be interesting to see if it survives Y2K.
The most lively area was always the SFRT now represented by DM.NET and SFF.NET.
Editor's note: As outlined by Lucy-S at SFF Net, that site was taken offline at the end of March 2017.