A few months ago, when iOS app extensions was make possible with an Xcode beta, I began writing a new app (in RubyMotion, of course) that included an iOS action extension that worked with the built-in Photos app. The tools were unstable at that point and app extensions frequently crashed or were not easy to attached to for debugging. Combined with the need to test on the device, I had to resort to logging extensively from the extension while debugging.
Long story short, I built mLogger to help. It's basically a networked version of NSLog+Console that runs on the Mac. Read the longer version of the story or download it here.
Suggestions and feedback are most welcome!