MjstkTumblr is a project mainly written in ..., it's free.
Allows easy use of new OAuth Tumblr API
Provides a simple PHP script which can be used in a a very simple way - ideal for AJAX applications. Once logged in you can utilise all of the API supplied by Tumblr
Documentation: http://www.tumblr.com/docs/en/api/v2
Example: mjstkTumblr.php?login to login mjstkTumblr.php?logout to logout
mjstkTumblr.php?method=user/dashboard
mjstkTumblr.php?method=user/dashboard&limit=1&type=photo
mjstkTumblr.php?method=blog/{blog-url}/info
mjstkTumblr.php?method=blog/{blog-url}/posts
mjstkTumblr.php?method=blog/{blog-url}/posts/photo&limit=5