The last version of Apple’s developer tool called Dashcode is 3.0.5, and stopped working after OSX 10.7 Lion. So, if you have OSX 10.9 Mavericks like myself and you wish to run Mavericks, you’ll have to do a little hacking.
Using your favorite editor using sudo, go into the Dashcode application’s Contents directory and edit the following file:
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Look for the CFBundleIdentifier key. In version 3.0.5 it can be found on line 234. In the string that follows (line 235) change com.apple.Dashcode to com.apple.DashcodeLegacy as I have done above. Save the file and you will now be able to run Dashcode in Mavericks.