I realize this is an ancient thread, but just in case anyone else runs across this when searching for information about CrossFire on the Mac:
CrossFire does continue to work on the Mac. I am currently using it on OS X 10.11.1 (El Capitan). The most recent CrossFire release is based on Java 6, which requires installing a legacy Java runtime from Apple, but it still works.
The warning "CrossFire.app can't be opened because it is from an unidentified developer" is the result of Apple allowing by default only apps from registered Apple developers to run. It is easy to work around: when the dialog comes up, you may click the "Open" button to open the app anyway.