Valve, the company behind Steam and many popular games such as Half Life, has released a mobile interface for their videogame distribution client. The app is available on iOS and Android, and allows players to connect with friends, message others with Steam chat, and browse the Mac and PC game library.
Keep in mind that mobile games are not available through the client since Apple generally frowns upon that sort of thing. The app is free, and available through the App Store and Android Market.
With the free Steam app for iOS, you can participate in the Steam community wherever you go. Chat with your Steam friends, browse community groups and user profiles, read the latest gaming news and stay up to date on unbeatable Steam sales.