It's based around an online service for storing and searching your notes along with browser bookmarklets for Internet Explorer, Safari and Firefox and stand-alone applications for Windows, Windows Mobile and Mac OS X (Leopard). You can also e-mail notes directly into your account and they're working on iPhone and SmartPhone versions.
Every note added to Evernote goes through powerful recognition and indexing servers, which make it possible to find everything. For example, you can search and filter on tags, titles, text, dates and even text in images or attributes like does the note contain a web clipping, an image, audio, handwriting, etc.
Evernote is in private beta at the moment but I've got a few invites to dish out if anyone wants one and you can request one from their home page. There will be free accounts available once the service is launched but online storage will be limited at 1Gb for these. Not a serious limitation for most small or personal research projects so it's definitely worth checking out.
There are alternative note-taking systems out there such as SpringNote, Google Notebook, notesake, Jjot, Scrapbook and Clipmarks but Evernote seems to cover a wider range of functionality and devices and the search and text recognition facilities seriously gives it the edge over anything else.
Related Posts: Capture The Web While You Surf!