Well there is ISBoxer. It has lots of features that can rotate which slave interrupts. Basically you can spam that one key and it send the key first to window 2, press it again sends it to window 3, etc... Down the line until it goes back to the first window.

There's some add-ons out there, but I've been on a WOW hiatus and not sure which ones are up to date. Deadly Boss Mobs also known as DBM was one I use to use.