Cantrip is a client for connecting to Multi-User Dungeons/Domains/Dimensions, otherwise known as MUDs. MUDs are, put simply, online multiplayer text-based adventure games. There are hundreds of MUDs that one can play, most of which for free. If you would like to try one out, check out The Mud Connector
If you would like to help out with the production of Cantrip in any way, just send an email to the developer.