For an introduction to Interactive Fiction, see http://brasslantern.org/beginners/introif.html.
Put simply, Interactive Fiction means text adventure games like Colossal Cave or Zork, but written these days generally for free in special-purpose languages. Again, see the introduction above and the entire BrassLantern.org site for more details.
I have written two IF games, Small World and Rematch. They were both written in TADS 2. I still have vague hopes of one day working on my long-delayed game Colossus, written in TADS 3, but...well, don't hold your breath.
In addition to games, I have written some source code for a module called TADSMap, which implements dynamic, graphical mapping in TADS 2 games.