I only recently noticed this, but of course it has been around for a little while now, and according to the description below it should work alongside the iOS version, although I don't think those have been updated in a long long time.
Link to iDrum for the iPhone and iPod touch
Take your beats anywhere! iDrum versions for the iPhone and iPod touch platforms are available now on the Apple App Store . iDrum now lets you share kits and sounds with your iPhone/iPod touch. Create beats in the palm of your hand with your own samples and custom kits!
The OSX app is priced at $19.99