Let's say I have the domain bob.com. I want people to be able to create a free subdomain (e.g. mysite.bob.com) and redirect it to their website. They would want to use this if their site has a long URL because they are using free hosting or something.
Its easy to do with PHP.. 1. Just store those users ID in mysql (like sub-domains) 2. Use mod-rewrite or htaccess for subdomains or perhaps you can use a script (like URL trimmer) to redirect. The script is here