For the first week, all non-game software on Steam will be offered at a 10 percent discount, a deal that expires on October 9th at 10AM Pacific Time. Launch titles include:
ArtRage Studio Pro
As time goes on, Valve will add more non-game software to Steam, though it remains to be seen if it will venture beyond mostly game-related content. For the time being, the above is what there is to choose from, many of which will take advantage of popular Steamworks features, like easy installation and automatic updating.