Hi yophie, yes like Eddi writes above it's a part of the edit frame functionality. If you click on that rotation arrow part of the edit frame, it will bring up the "wheel mode" of 3 circles you can use for doing rotations in other directions.

It's in the "edit frame" part of the documentation:
http://moi3d.com/3.0/docs/moi_command_reference11.htm#editframe

Also when you are in "wheel mode" you can drag on the rotation center point to move it somewhere else to rotate around a specific point.

For controlling it, if you click and drag on a wheel you'll do a rotation of the object and if you're in the 3D view you can do that on an y of the 3 wheels to do the rotation around different directions quickly.

- Michael