Objective C, sure, but cross platform, thanks to Cocotron, an open source implementation of the Cocoa API. http://www.cocotron.org/

It's the first Cocotron-based project I see featured on HN, although it's not the first success story that they could brag about...

See also: the account of the porting of the File Magnet Uploader, then Mac-only, to Windows, using the same library. http://macdaddyworld.com/2008/10/27/adventures-in-cocotron/