I don't know.
But I'm curious about how far you'd take the non-commercial thing.
"Bob's Widget Sales" would probably be commercial.
But what if I link to the "Bob's Widget Sales" site from my hobby information site, does that make mine a commercial site?
Where does the line get drawn between commercial and non-commercial?
You're right, that would get very difficult to draw the line. It seems that no matter where you draw it, people would still find a way to cross it.
What is it exactlly "non-comercial site" if you have dosens of poems of Vladimir Mayakovsky at your site and do not sell books only link to "amazon" you should be considered non-commercial?
It's not possible.
Even assuming you were as wise as Solomon, to carefully weed out all intersections of that 'pure' knowledge which is perfectly untainted by any form of commerce, and you had a billion monkeys or geeks at a billion typewriters for a billion years...maybe.
You could theoretically do it with an entirely human-edited engine, except that an entirely human-edited engine which is also relevant or more than barely functional is a complete and total impossibility (and that, I dare to say, includes the flawed DMOZ directory, which is the closest to such a creature we've ever seen).
wikipedia is another good example of human edited project and they fight spammers every day. Now most of time they spend editing spam in their database.
Search engine profiling (like google scholar) is good way to go.
There are search engines for government sites, charities, support groups and other non-profit groups. These are certainly non-commercial.
I'm not aware of an all-inclusive entire web search engine with the criteria of anything but commercial. It would be a neat project, but would require human editing. The point of it seems a little weak though, as if I'm looking for info on bicycling I probably want to see a bike manufacturer or two in the mix.
Now a search engine with no dealers, affiliates, or intermediaries would be really useful!
even a site consising of
can be considered advertising previous browser, that did not show empty pages ;)
I was going to mention Zeal as well. You can't get any commercial site past their editors. If accepted your site gets included in the LookSmart directory however I am not sure if they are separated in any way from normal websites.