Experimental search engines

Based on this comment by Gaurav in a previous thread, I decided to list out some experimental search engines that I know of. These are search engines that are in development, beta, or dont index large portions of the web. Here is my list -

New MSN Search (Beta)
Teoma
Mooter - Web Search
Kartoo
Vivisimo clustering search engine and Clusty (Beta)

It looks like clustering search engines are the hot thing to experimant with at the moment. I've tried a few searches with some of them, but the results are still generally not that great. Keep in mind that they are all still experimental / beta.

Finally, a couple of special interest search engines. These aren't general interest search engines, and there are thousands like them covering every imaginable topic, but I find these two to be the most interesting

Koders - Source Code Search Engine
Pi search: Search 4 billion digits of Pi :-)

Any more interesting search engines out there ?