Just found this one and it looks like a good choice for anyone who want to run their own tinurl service or just have a link cloaker for once affiliate links.

Code:

http://www.hido.net/projects/phurl/

It's a simple script but got some nice features like admin panel, captcha and duplicate url record handling.

As a free choice I think it got what one need for cloaking affiliate links.

Script Features:

* May handle billion of records (seperated SQL table structure, it depends on your server configuration)
* CAPTCHA (image) verification (configurable)
* reCAPTCHA support (configurable)
* Can run with or without mod_rewrite module (configurable)
* Can handle urls with or without http:// prefix
* Duplicate URL record handling
* URL prunning/cleaning via cron-job (configurable)
* Very easy installation
* Simple administration for record deletion
* Valid XHTML 1.0 Strict and valid CSS coded
* Free - Licensed under GPL