Posterous today announced a new API for all 3rd party developers, allowing them to access the full Posterous technology stack in their applications.

The API, previously available only to the Posterous engineering team, allows developers to create sites, add users to it and assign custom themes for each user. Additionally, it now has several new methods for retrieving and manipulating data around sites, users, posts, comments, and other Posterous data types.

Posterous API Posterous is now a full on WordPress Multisite rival with its new API

That aside, Posterous said that the new API conforms to the REST constraints and offers a clean and concise set of URLs for parsing and understanding purposes. Developers can also experiment with it by dynamically changing the parameters and inspecting the response on Posterous’s new redesigned API website.

One of the first users of this new API is Oxfam, which are using it to to drive awareness and participation in one of its recent campaigns, where users will be able to create a blog hosted on grow.gd with a custom Posterous theme and a embedded grow widget.

Competition with WordPress Multisite?

One of the significant changes this new API brings along is the ability to create new sites, which puts Posterous in direct competition with WordPress Multisite (earlier WordPress MU).

Although WordPress Multisite might offer more features than Posterous, many publishers and brands may simply jump into Posterous to create several custom made blogs on its domain, where they can simply post updates, skipping all the difficulties they would likely face in self-hosting a blog.

What do you think? Do chime in your thoughts and opinions in comments below.