Lessn is an extremely simple, personal url shortener written in PHP with MySQL and mod_rewrite. The installation is very simple with full instruction in a readme file. Lessn is offered free, as is, sans support and without warranty (but is really not as scary as all that).

Open /lessn/-/config.php in a plaintext editor and create a Lessn username and password then enter your database connection details. Upload the entire /lessn/ directory to your server. For the shortest urls, place it at the root of your site and rename to a single character. And then visit http://yourdomain.com/x/-/ to Lessn a new url and grab the bookmarklets.

Requirements: PHP 4.4.8+ and MySQL 4.1.25+
Demo: http://www.shauninman.com/archive/2009/08/17/less_n
License: License Free