TomHarrigan

This version requires Buddypress and YOURLS url shortener. Add tweet buttons to activity stream posts allowing users to ‘tweet’ the item. Shorten urls with your own custom YOURLS shortener. Other Url shortening services being added soon.

BuddyPress Tweet Urls

Adds custom tweet button to BuddyPress sites using YOURLS.

Boone Gorges

<a href="http://yourls.org/" title="Your Own URL Shortener" rel="nofollow ugc">YOURLS</a> is a free URL shortener service you can run on your webhost to have your own personal Bitly.
This plugin is a bridge between <a href="http://yourls.org/" title="Your Own URL Shortener" rel="nofollow ugc">YOURLS</a> and your blog: when you’ll submit a new post or page, your blog will tap into YOURLS to generate a short URL for it.
This plugin also features BuddyPress support. Short URLs can be generated automatically for each member and each group, and are customizable if permitted by the BuddyPress administrator.
Requires PHP 5.
Note: this plugin should still work but is no longer maintained. See http://yourls.org/#More#wordpress

YOURLS: WordPress to Twitter

Use YOURLS (a free GPL URL shortener service) to create short URLs of your posts, or for your BuddyPress groups and users

BuddyPress Tweet Urls vs YOURLS: WordPress to Twitter