Tool clusters and some selected criteria are on the edge of the circular diagram. Tool clusters are on the right, criteria are on the left.
Mouseover a tool cluster or criteria (see the list below the diagram) at the edge of the circle to focus on it. The links to/from the group you have selected will be highlighted. The total number of tools in the cluster (and their names) or the total number od tools matching the criteria you have chosen will appear.
The thickness of links between tool clusters and criteria encode the absolute number of tools from a given cluster that match a given criteria. Mouseover a given link to get quantitative information.