rp.ly can host a URL shortening database on any domain name or sub-domain. This article will walk you through the rp.ly offering and explain how to set up your own vanity URL shortener to promote your blog posts and improve the branding and permanence of your shared items.
After you log in to http://rp.ly with Twitter OAuth or Facebook Connect, you will see an empty list of your personal rp.ly URL shorteners. Click the “Create a new URL Shortener” link to continue.
In this example I’m creating a custom URL Shortener using a domain name that I already own, “bh.ly”. rp.ly will generate custom URLs using my own empty shortcode database, here’s an example: http://bh.ly/1.
But for this demonstration i’ll assume you don’t have your own domain name to use, thats OK you can just use your rp.ly subdomain. Now rp.ly will generate short URLs for me like this http://me.rp.ly/1 and I can change the settings later to use a “vanity” domain name of my own.
Now I have my own URL Shortener at rp.ly, I can start making custom short URLs. Here I’ve pasted “http://wordpress.com” into the Shorten box.
When I click the “Shorten” button, rp.ly accesses my personal database of Short URLs and creates a new shortcode and Short URL. Having my own shortcode database means that no-one can “impersonate” my Short URLs, which is a problem with solutions that share shortcodes between “vanity” and normal Short URLs.
Here I am putting my rp.ly username and password into my WordPress blog settings, after I installed the WordPress plugin (available at github.com http://bh.ly/0h) << see how I linked to that with a “vanity” Short URL? 
Now I can compose a new WordPress blog post, I know that when I hit “Publish”, rp.ly will generate a nice custom Short URL for me, and Tweet the headline and Short URL to Twitter to promote my blog post.
Here is my Tweet!
And for me this feels like a Jobsian “one more thing…” moment, because I think this is pretty awesome, but you may have noticed there is a link to a “microblog” for your rp.ly shortener. Fundamentally, a URL Shortener is a feature of a microblog, and that’s how we’ve designed it here at rp.ly. rp.ly is 100% open source, allowing similar providers to pop up. Your microblog and Short URL data are yours and will be compatible with other providers.
Clicking the “microblog” link will take you to your new/empty microblog, which has been pre-configured to use the URL Shortener you created. This microblog should actually have my WordPress Tweet/post on it, but I changed the order of this demonstration around a little bit.
Now i’m logged in with Twitter OAuth and I can play around with my new open source microblog, I am the Admin. This microblog can be a full two-way Twitter client too, that feature, including showing my Twitter friends and enabling real-time Comet-push delivery, will be enabled at rp.ly soon.
If I click the “Add: Link” button, I get a FriendFeed-style pop-up window, and I can paste a long URL in there.
The microblog makes a remote AJax call to the rp.ly tr.im-style json/xml API to create this short URL. If I have configured a vanity domain name for my Short URLs, I will see it here.
Now I’ve created the first Tweet on my microblog, and the Tweet was not only sent to Twitter, but has also been pushed out to any of my Followers on the OpenMicroBlogging network of decentralized OAuth-enabled microblogs. It will have RSScloud and Pubsubhubbub soon, as well.
Here is what my Tweet looks like from Twitter.
Well, I can’t believe you made it this far! You must think rp.ly is very interesting . So do I, please let me know in the comments if you have any ideas or questions. Thanks!