There is a cool blog article on Evernote's blog
that discusses how some third parties are using the Evernote API to integrate into their applications. One of the interesting items is from Tarpipe. Tarpipe simplifies the process of adding, sharing, and moving content among the web services you use, by allowing you to define a repeatable, automatic workflow. The Tarpipe/Evernote integration allows you to add content into your Evernote account, as well as automatically extract content, such as recognition data and URLs to public notes, which can then shared with other supported services. Check out the Evernote blog post for details on a Tarpipe example where you can create a workflow, in which an email subject becomes a Twitter message, that is then automatically sent into Evernote to create an archive of your tweets. Neat stuff.
The other third party is Pelotonics which is a project management and collaboration service, which allows organizations to easily manage multiple projects and tasks among groups of users.