Expert Sleepers has released the Mac OS X VST and AU versions of Clocker - a free utility plug-in that sends MIDI clock.

Why would you want a plug-in to send MIDI clock when your host app sends MIDI clock perfectly fine? Well, with Clocker you have a separate, adjustable source of MIDI clock. So you can send all kinds of crazy tempo to some of your outboard gear, while the rest of your stuff plays back in time as usual.