SlightBBS
A simple, light telnet BBS for Linux
...Written in PHP and MIT licensed, slightBBS is the solution if you want a telnet BBS that isn't a pain in the neck to setup. Based on sdf.org's "bboard" system, slightBBS uses simple commands and provides a way to socialize via your terminal software.
Supports easy localization, if you want to setup a bbs that isn't in English. Works with STDIN/OUT, so you can set it up to work on almost any system; it will even work at the command line, with few modifications.