Posterous, the startup which operates a dead simple blog that enables users to post updates via email to post@posterous.com, has launched a new tool called post.ly.  If you're a Posterous user, you probably have seen post.ly in shortened Posterous URL's.  

Here's how it works.  If you head to post.ly, you'll see this simple interface which lets you write out a tweet.  Below you'll notice a button to upload a file.  Post.ly lets users upload photos, music, video and documents, then optimizes that file for viewing on the Web, all for free.  Post.ly makes it easy to connect to your Twitter account using the OAuth protocol.  Post and your set. 
If you're a new user, you'll notice the shortened URL takes you back to your very own Posterous blog, which you can then customize and make look however you want. 
"We built post.ly to teach more people about Posterous. It was built using the Posterous technology stack in just over a week. When you post using post.ly using Twitter credentials, it's creating Posterous site for you, using our rich media technology, autopost, and more," Sachin Agarwal, co-founder of Posterous told VatorNews.  "The goal is to teach people about Posterous."
Posterous told us it differentiates itself from similar services in several ways:  It's ad free, and you can put your media on your customized site and on your domain.  

Agarwal shared one more bit of news with us about Posterous saying we should expect to see a pro version later this year.  

If you want a behind the scenes look at Posterous and their startup culture, check out our feature, The startup culture at Posterous.