Telehack is a simulation of a stylized arpanet/usenet, circa 1985-1990. It is a full multi-user simulation, including 26,600+ simulated hosts 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. Telehack is an interactive virtual museum that allows one to see what the Internet was like in the 1990s, when young hackers were browsing through different bulletin board systems and shell accounts. One can learn exactly how they hacked in a safe and simulated environment as well as view real documents saved from BBSes thanks to textfiles.com.
Text source: https://en.wikipedia.org/wiki/Telehack