IntroComp is the only competition I’m aware of for unfinished games (specifically, text adventures). Each year for the past eight years, programmers have submitted incomplete versions of their games to be judged. Judging is performed by peers, which could mean you!
Every IntroComp entry is available for download, and once you play them, you can vote on them. Now I know what you are saying — how much will it cost me to download and play incomplete text adventure (now referred to as “interactive fiction”) games? The answer is, it’s free! If you used to play or dabble in text adventures back in the day, this is a great way to both play some new games and give some hard-working programmers some much needed feedback. The writers of these games cannot collect their prizes until the games are finished, so this really helps them out.
As a bonus, playing these games will no doubt get you in the mood for Get Lamp, Jason Scott’s upcoming documentary about text adventures.