Steam's game approval service Greenlight has expanded to include a new service called "Concepts". Concepts allows a developer to post up their game for free so that the developers can gauge interest in their game and potentially form a community of interested gamers. However, Concepts will not allow a game to be added to Steam; that will require paying the $100 fee (donation to Child's Play) to get on Greenlight proper.
As you can see from the quote in the image, Valve says that "this section is intended for items looking to gather feedback from the potential customers and begin building a community."
The ability to drum up support on Steam free of charge should certainly be of interest to indie developers, as some games in the past have had to release outside of Steam to gain a community before having a chance to be on Steam (an example of which can be found in this Joystiq piece). Concepts certainly looks to be a promising compromise to assuage developer concerns and let Steam users interact with and help shape more games.
Source: [Steam Greenlight]