Clocker
Why would you want a plug-in to do that, 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.
It's a niche requirement, granted.
Oh, it's free, as in beer.
Download from the downloads page.