Greenlight? Red light.

Steam is many things, at least if we're talking about the Valve games and DRM platform, which also doubles as a store-front. It's a clever piece of software that now runs in the background on the majority of gaming PCs. It has pushed forward digital distribution to an amazing degree, and it's competitors are still trying to catch up (unfortunately that might be impossible, due to Steam having a very dominant place in the market). It's a tool of marketing genius, which has many gamers checking for new deals and new games to buy and download from the comfort of their own homes.

For the independent games development community, it's been a massive boost to sales. Having such a large marketplace allows developers of a niche games to find their audience, and being on Steam can have a large impact on the relative financial success of a project.