Telehack is a simulation of a stylized arpanet/usenet, circa 1985-1990. It is a full multi-user simulation, including 25,000 hosts and BBS's from the early net, thousands of files from the era, a collection of adventure and IF games, a working BASIC interpreter with a library of programs to run, simulated historical users, and more.

Read more here:
http://telehack.com//