The IUBMB developed the EC system of nomenclature and classification of enzymes based on the reaction they catalyse. This is a hierarchical system. It is displayed below using the Hypergraph applet, as a 'tree' in a hyperbolic geometry.
Click on a node to center it (or, if your computer is faster than mine, drag the node to center it). Clicking on a terminal node, or 'leaf', will bring you to the enzyme commission's page on that enzyme (which has further links to related databases).
The data used to create the hypergraph was 'scraped' from the web pages of the enzyme commission. In general, this is bad practice, but since it only involved downloading 12 or so pages, and furthermore, a flatfile containing the relevant information was not available for download, it seemed reasonable enough. I created a flatfile from this data (use at your own risk - may contain errors - probably is out of date) [ECflatfile.txt].