Tumblr calls itself "the easiest way to share yourself" online. With Tumblr, you create "Tumblelogs," which are, essentially, online scrapbooks. Tumblelogs can include photos, videos, audio, messages, quotes, links, and chat dialogs. Tumblr also now provides the Tumblr API, which lets you programmatically read and write Tumblr data. The API is REST-based, with XML and JSON data format options, and supports both read and write functionality.
To retrieve Tumblr data in XML format, you append the user's Tumblr URL (for example http://KalaFarnham.tumblr.com) with "/api/read" (for example, http://KalaFarnham.tumblr.com/api/read). To retrieve the data in JSON format, append "/api/read/json" to the Tumblr URL. Additional options let you specify a range of Tumblr posts or a type of post (regular, photo, etc.).
The Tumblr API write function creates new Tumblr posts. Each request must include authentication (the user's login name and password). The authentication, post content, and options are encoded into a standard HTTP POST request. See the Tumblr API documentation page for details.
As an example, the Tumblr Wall Facebook mashup application lets Tumblr interact with your Facebook account (and as you can see in our profile listing, this was created by prolific mashup developer Sebastin Sanjay who has created over a dozen mashups using 13 different APIs).
Tumblr is an interesting variation in online sharing and social networking, backed by a simple but complete standards-based API.