A colleague of mine just started a website called wikiquation.com. It's a searchable wiki-style database for equations. The database is currently quite empty, so it's not very useful as a search engine yet, but it allows anyone to add or edit an equation without creating a user account. I think the site has some serious potential, since it's pretty hard to find an equation on the internet unless it has a specific name (assuming you can remember it). His website allows you to use both words and variables as search input (using LaTeX for non-keyboard symbols). At the very least, it could be useful as a personal equation resource. I thought it was pretty cool, so I thought I'd share the link. http://wikiquation.com" [Broken] Since this website is a nonprofit and science-related, I believe this post falls within the forum rules on advertising (see below). If I have misinterpreted these rules, please remove my post and accept my apologies.