It seems like you might be able to get a free copy of Postal 2 on Steam/Desura if you Greenlight its release. Anyone who helps to promote it should get a free key, which is just awesome:
"Simple really, if you post about our Greenlight somewhere other than Steam, such as on popular forums you already have an account with* (4-chan, Reddit, PCGAMER, Rock Paper Shotgun, Giant Bomb ect) and post the link here, I'll make sure you are one of the first to get a key for POSTAL 2! Also applies to your personal pages** ( facebook, a blog, youtube ect).
If you post it to multiple places, I'll make sure you also get a free P1 desura key.
As of now, we don't know 100% know if we can give out free Steam keys, if not I'll make sure you get a Desrua Key instead and a link to all the extras we give away on GoG.com. If we can give out Steam keys, the only group currently promised them (due to the difficulty of quickly proving ownership) are the regulars at the RWS Forums, so this is an alternative way to be included in that priority group."
They aren't 100% sure you'll get keys :P