FCP 7 on Mac OSX 10.10 Yosemite
I've tested this on new MacBook Pros, older MacPros, and new cylinder MacPros, iMacs, and FCP 7 continues to work. So, while Apple officially discontinued selling and even developing for FCP 7 (and Final Cut Studio), the software still works. Of course, any bugs or issues present in FCP 7 as of June 2011, will still be there and never get fixed.
I've found some issues in DVD Studio Pro like colours of buttons aren't visible in the drop down menu, and Cinema Tools is often unstable. But otherwise it works.