I've been doing only iOS development and never made an OSX app. In the iOS project I'm working on now I see that suddenly Xcode thinks it's an OSX project. The all my framework files are shown in red (missing), and lots of the options in the project panel show choices that are only appropriate for OSX such as "deployment target", which offers only 10.4, 10.5, 10.6 etc. and in Build Settings the Valid Architecture shows i386 x86_64 with no drop-down options.
What happened? How can I change this back to an iOS project?