Its more than STEAM…its xStream.
The “x” makes it sound cool….and so does this feature:
“3D Realms choose to work with Game xStream because their service is not only highly flexible, meaning that a whole list of features can be either used or not, but because it allows what in my opinion is the most important feature of all, and one that Steam does not support: A player can buy a game, and within minutes start playing it, without needing to download the entire game. For example, I can start downloading the Doom 3 demo — one of the most content intense games currently available — and within six minutes I’m playing it as if I have the full game, racing like a madman through the opening level, while the game continues to download itself in the background. (You can not catch up to where new content isn’t available.) ”