Frotz is a Z-Machine interpreter; in short, a program for playing text-based adventure games. If you've played classics like Zork or Hitchhiker's Guide to the Galaxy, you'll know what to expect. (Unfortunately, these two specific games are not available on ctrl-c.club, since they are commercial works).
Fortunately, there is a robust community making modern text-based adventure games (which are now called Interactive Fiction). Many games are available for free from the Interactive Fiction Archive. A few of our Ctrl-C.club members are writing their own IF right on the server using the Inform 7 programming language!