The concept category lets developers submit games that are still in their very early stages in order to receive feedback and build a community before development even begins. Users can still vote on projects in the concept category, but the votes will only be used as feedback for developers and will not go toward getting the game distributed on Steam.
Greenlight has also added a software category, allowing developers of non-game software to submit their programmes to receive feedback and have the community vote for Steam distribution.
The new Greenlight category will help Steam build its library of non-game software titles, which it just began offering earlier this month.
Thirty one games have been approved through Steam Greenlight so far, including the fan-made Half-Life remake Black Mesa and the bizarre domestic stealth game Octodad: Dadliest Catch.
Only one game has actually released from Steam Greenlight, McPixel, which is available now on Steam.
> Read Digital Spy's review of McPixel (iOS)
Watch the trailer for Octodad: Dadliest Catch below: