Here is a list of them:
[link|http://www.dmine.com/telnet/|http://www.dmine.com/telnet/]

GameSVR can help a FOSSIL based BBS get access via Telnet:
[link|http://www.mannsoft.ca/gamesrv.php|http://www.mannsoft.ca/gamesrv.php]

It works with WWIV 4.30 for DOS, they have a Howto for WWIV. I imagine it would work for other BBSes as well to get them Telnetable.

I recently put up my old BBS via GameSVR as a test. It works, but the games don't seem to function.