A new fan game is under way, Star Trek Adventures The game is set in an episode from TOS and they have a demo out. This from their site "The mission "Arena" takes place on stardate 3045.6 and is based on episode 18 of Star Trek The Original Series (also titled "Arena").  In this game you will relive the events of the episode as you must beam down to the ambushed colony called Cestus III and locate any survivors who may be able to give you clues to what has happened.

Among solving the mystery as to what happened on Cestus III you will engage in a space battle with an unknown enemy ship.  Upon your encounter with the Metrons, you (as Captain Kirk) will be beamed down to an uninhabited planet to go face to face with a Gorn captain. You will have to use your brains and environment to solve puzzles and build a weapon that will allow you to stop the Gorn."

Looks pretty good so far, pop over and give the guys some support.