Update: The app is now open to all Steam Users.
Valve has released the Steam Mobile iOS and Android app, allowing Steam users to keep in touch with other users without the need to access the PC client.
The app will allow Steam users to chat with people on their friends list, as well as browsing the Steam catalogue to add stuff to their wishlist, stay up to date to discounts and offers and score themselves a Steam title while on the go.
Steam Mobile is currently in closed beta testing and gamers can express their interest simply by logging on to the app, which is free. They will be added as the testing progresses.
For more information on Steam on Mobile, head here.