Joe Presbrey wrote the crawler, a 7KB bit of Python called walk.py which uses my own somewhat old rdfxml.py to parse RDF/XML (which I was rather surprised about). It's multi-threaded, and runs very quickly indeed: it takes just 32 seconds for it to spit out all 12 OpenIDs currently within three hops of the DIG members:
http://en.wikipedia.org/wiki/Mesh_networking
