The Steam Beta is a test server available only on Steam.
It was first used to test Sledgehammer and is rumored to be used to test the features coming when RCF upgrades to Unity 5.
The Steam Beta was first used to test Sledgehammer along with the missions & achievements. It included all the existing features in RCF, and some new features. However, the shop was outdated, with the vehicle store missing the Chieftain, Leopard 1A5, and UH-60 Black Hawk.
The Steam Beta is rumored to be used to test RCF for when it is upgraded to Unity 5. It may also see a return of the jets, as well as Island X and a new oceanic test map.