GDC has been a bonanza of announcements for free-to-use engines, with Epic’s Unreal 4 coming with no costs other than 5% share of any revenue, and Source 2 being completely free.
Whilst Source 2 won’t demand any cut of your profit though, it does come with it’s own smallprint: any game made in Source 2 must be sold on the Steam store.
Talking with Rock, Paper, Shotgun, Valve’s Erik Johnson explained that it is mandatory for Source 2 games to appear on Steam, which presumably is to ensure that Valve are able to pick up revenue based on Source 2’s use (anything sold on Steam sees 30% of the revenue taken by Valve).
Whilst a Source 2 game must be sold on Steam, it doesn’t have to be exclusive to the platform. You can sell anywhere else; be that other client platforms, digital stores, or in physical, meaning that even if that 30% cut seems deep, you can make up for it in sales from other outlets.
Of course, using the Steam platform grants access to Valve’s DRM systems, multiplayer matchmaking, and the Steam Workshop, all which may be key to a developers idea. Even if they’re not, few things are more tempting than saving money in the world of development.