Do some research into the old BBS (Bulletin Board Systems). What you're talking about is similar to that. They would have people call in (either one-to-one or one-to-many), post on a forum, chat in chatrooms (for those with one-to-many options) and a variety of other things including games. It's entirely texted based and usually was for the Windows-platforum.

Doing a search on google for "BBS Software" should pull up some results. The BBS Software Directory may also help. Just so you can get ideas. One that I remember is Sapphire. It was developed by a friend of my uncle's (this guy also developed a game I used to play called Pyroto Mountain -- which was a text-based BBS game)