Uuid is a project mainly written in PHP, it's free.
Experimental fork of UUID module from Drupal.org
Generate Universally Unique IDentifier (UUID) for Drupal objects.
Current features include:
* Automatic UUID generation/loading/deleting for nodes, node revisions,
users, roles, files and taxonomy.
* Transparently create UUIDs for objects which don't have one.
* Pluggable UUID generator backend.
* Sub modules to enable UUID for different entities.
* API for implemening UUIDs for contrib entities.Please read uuid_ossp/README.txt before enabling the uuid_ossp module.