Nikolay Kolev

The ShortURL plugin allows you to use your blog as your own URL shorterning service by implementing the <a href="http://wiki.snaplog.com/short_url" rel="nofollow ugc">Short URL Auto-Discovery</a> specification. Your short URLs will be in the form of <code>http://domain/-code</code>.
The auto-discovery feature allows third-party services that honor it to use your own short URLs instead of generating new ones using services such as <a href="http://tinyurl.com/" rel="nofollow ugc">TinyURL</a>, <a href="http://bit.ly/" rel="nofollow ugc">bit.ly</a>, and others. This gives your posts and pages canonical short URLs that give you all SEO benefits and don’t leak traffic out to external domains and will prevent linkrot. The homepage short URLs is set to just <code>http://domain/</code> as a unique feature.
The other great benefit of the ShortURL plugin is that the generated short URLs won’t break if you change the permalink structure of your blog or rename the slug of a particular post or page.
Due to the recent choice of both the <a href="http://microformats.org/" rel="nofollow ugc">Microformats</a> community and <a href="http://wordpress.com/" rel="nofollow ugc">WordPress.com</a> to use <code>rel="shortlink"</code> vs the alternative proposals, the ShortURL plugin is also using it now.
More on the topic:
<ul>
<li><a href="http://microformats.org/wiki/rel-shortlink" rel="nofollow ugc">Microformats Wiki: rel=”shortlink”</a></li>
<li><a href="http://en.blog.wordpress.com/2009/08/14/shorten/" rel="nofollow ugc">WP.me – shorten your links</a></li>
</ul>
<h3>To Do</h3>
<ul>
<li>Test against <a href="https://wordpress.org/" rel="ugc">WordPress</a> 2.9 and <a href="https://mu.wordpress.org/" rel="nofollow ugc">WordPress MU</a></li>
<li>Add a settings page</li>
<li>Add a widget</li>
<li>Integrated with <a href="http://www.google.com/analytics/" rel="nofollow ugc">Google Analytics</a></li>
<li>Integrate with the top <a href="http://twitter.com/" rel="nofollow ugc">Twitter</a> plugins to use ShortURL instead of third-party services</li>
</ul>

ShortURL

The ShortURL plugin provides short canonical permalinks to your posts and pages similarly to WordPress.com via its WP.me service.

akrabat

The Shorter Links WordPress plugin overrides the default WordPress 
“shortlink” URL with one that has a custom text in it. You can also set a 
different base URL.
A custom field called “Shorter link” is created once a post is saved, 
so that you can change the shortlink to a more memorable set of 
characters.
The choice of base URL to use for the short link can be configured within 
Settings->Shorter Links.
Related Links:
<ul>
<li><a href="http://akrabat.com/shorter-links" rel="nofollow ugc">Plugin home page</a></li>
</ul>
<h3>Licence</h3>
This plugin is licensed under the <a href="http://akrabat.com/license/new-bsd" rel="nofollow ugc">New BSD license</a>.
<h3>History</h3>
2.1.0 – 8 August 2015 
Rework to look for the shorter link after WordPress has done its processing. This 
means that a shorterlink that represents a date won’t affect an archive list.
2.0.6 – 8 August 2015 
Ensure that the short_link is correct when using a post id.
2.0.5 – 8 August 2015 
Updated Tested up to 4.3
2.0.3 – 9 July 2012 
Bug fix so that archives work.
2.0.2 – 23 June 2012 
Fall back to REQUEST_URI if there’s nothing interesting in $query_vars.
2.0.1 – 20 June 2012 
Updated to handle 4 digit short links that look like a year to WordPress.
2.0.0 – 21 November 2010 
Updated to be WordPress 3.0 or above, so we only need to hook into the WordPress 
shortlink system
1.8.2 – 21 November 2010 
Fix permissions issue on settings page. This is the last version that works 
on WordPress 2.9.x or earlier.
1.8.1 – 7 September 2010 
Bug fix to remove a warning.
1.8 – 1 September 2010 
use shortlink rather than shorturl for WordPress less than 3. 
For WordPress 3 or higher, hook into the new shortlink system. 
Fix the admin page so that it displays in WordPress 3.
1.7 – 11 Feburary 2010 
Handle failures better.
1.6 – 10 January 2010 
Update version number in correct places so that the WP plugins system notices the update.
1.5 – 29 December 2009 
Support permalinks that start with /%category%/
1.4 – 14 April 2009 
Support rel=”shorturl” as per <a href="http://sites.google.com/a/snaplog.com/wiki/short_url" rel="nofollow ugc">Robert Spychala’s Short URL Auto-Discovery proposal</a>.
1.3 – 14 April 2009 
Add support for setting the base URL. Patch by <a href="davemastergeneral@gmail.com" rel="nofollow ugc">Dave Marshall</a>.
1.2 – 13 April 2009 
Only send the <code>Link</code> HTTP header as recommended by <a href="http://shiflett.org/blog/2009/apr/a-rev-canonical-http-header" rel="nofollow ugc">Shiflett</a>.
1.1 – 13 April 2009 
Fixed output of HTTP headers. Patch by <a href="http://bethesignal.org/" rel="nofollow ugc">Jeff Waugh</a>.
1.0 – 11 April 2009 
Initial release.

Shorter Links

Override the default WordPress "shortlink" URL with one that has a custom text in it. You can also set a different base URL.

ShortURL vs Shorter Links