What’s your favorite MMO plugin?

When I went back to Lord of the Rings Online a couple of weeks ago, I spent a decent amount of time searching the internet for my favorite plugin. Initially I couldn’t remember its name, and as I had built a new computer since I last played LotRO, it wasn’t installed or archived on a local drive.
It’s called TonicBars, and even though it hasn’t been updated since 2012, it still works and it’s a godsend if you want to de-clutter the game’s busy UI while maintaining easy access to a ton of hotbars that only appear when certain customizable conditions are met.