Using Kaleidoscope with PhpStorm
Eventually sussed it - if anyone comes here in future, you want to install KSDiff (also available from the Kaleidoscope site), then go to the External Diff Tools tab in Storm, and set it up as:


External Compare Tool: /usr/local/bin/ksdiff
Parameters: %1 %2


Then open Kaleidoscope and leave it running - if you don't, nothing will happen.