Linux/Mac/Windows: One of the things that makes Evernote one of the best note-taking tools around is its availablility on multiple platforms. Linux, however, has long been left out of the equation, but now Linux users can keep their notes in sync with Nevernote.
While it is now possible to install Evernote on Linux with WINE, it isn't exactly ideal. Text encryption, for example, doesn't work in WINE, and installing apps in WINE isn't always fun (nor do the results look very good). If you'd like to access Evernote somewhere other than your browser, open source Evernote clone Nevernote might be a good option.
Not only does it have most of the features of the Windows and Mac client, it also has a lot of features you won't find in the Evernote client, like database encryption, hiding notebooks, multiple databases, inline PDF view and a bunch more. It is a Java app, which some people won't like, but if you want to use Evernote on Linux it's probably your best option (Java also means Mac and Windows users can use it too, if you want some of the Nevernote-specific features).
Nevernote is a free download for all platforms.
Update: The link on Nevernote's home page seems to be down. You can download the program from its SourceForge page.