Sociable for iPhone enables posting to multiple social networks at once, add all of your Twitter, Facebook, LinkedIn and Tumblr accounts and selectively post to all or some of them.
Upload photos to Twitter (TwitPic), Facebook and Tumblr, and optionally geotag your tweets with your current location.
I designed the user interface, and developed the application using native Objective-C and Cocoa.
Sociable is now at version 2.0, and available on the app store around the world for $0.99 (69p).