Elias Torres - WP-APP: Atom Publisher Protocol for WordPress:
"Simply drop app.php into your root wordpress install directory and have some Atom/APP fun.
If you don’t have wordpress installed, I’ve setup a demo server for you to try it out. First, register to get your own account, since you won’t be able to post/put/delete entries without a valid username and password. The rest is all curl geekiness for those who care."