While no official desktop client exists, there are a couple of options, the best of which, to my mind, is Everpad. There's also an open-source clone in NixNote, but I've found it to be clunky and a bit of an eyesore. You can also create a website-specific application with Chrome or Fogger. In my experience, a combination of Everpad and an Evernote Fogger app is the best solution, and of course browser addons exist to further enhance the Evernote experience on Linux.