There's a follow-up to Valve's announcement of the free Source Engine 2 on Rock, Paper, Shotgun, where they talk with Valve's Erik Johnson (inaccurately promoting him to "studio founder" along the way), who explains how Valve will make money while giving away their development tools. Erik explains that Source 2 games must be made available though Steam, which will pay Valve a 30% commission on all sales. There is no exclusivity to this, however, so said games can also be sold elsewhere as well, with no additional proceeds to Valve. They hash through what might be the best option for small developers choosing between Unity 5, Unreal Engine 4, and Source 2, all of which have recently introduced new business models making them all more affordable.