I just bought one. It is an attachement for my longarm machine allowing me to do Squircles, Circles, Feathers, Wreaths, and all kinds of Watchamacallits. It will take my longarm quilting to a new level.
What does it do? Check this out, these are just a couple of samples borrowed from the Circle Lord website
I can't wait to get going on it. Stay tuned, I will have to come up for air sometime, and I will try to post once in a while.