Tools > Align Nodes in Circle
Move the selected nodes into a circle.
At least four nodes need to be selected for default behaviour.
There are also some special cases:
- When one node, part of a way, and this way are selected, then make a regular polygon.
- When one way and one separate node is selected, set center to position of that node.
- When one more node, part of the way, is selected, set the radius equal to the distance between the two selected nodes.