Cross ROADS: Cross-searching ROADS-based subject gateways: http://www.ilrt.bris.ac.uk/roads/cross
HotOIL: http://www.dstc.edu.au/cgi-bin/RDU/hotOIL/hotOIL
Inference Find: http://www.inference.com:80/ifind/
MetaCrawler: http://www.metacrawler.com/index.html
MetaGer: http://meta.rrzn.uni-hannover.de
ProFusion: http://www.designlab.ukans.edu/profusion/
SavvySearch: http://www.cs.colostate.edu/~dreiling/smartform.html