I make heavy use of vnet jails in FreeBSD at work. Due to FreeBSD's rc.d system not supporting vnet jails well, I opted to create a little command-line PHP project to make administration of jails easier. Though the tool was useful, it lacked in flexibility and usability. After learning how to write modules for Drupal, I opted to rewrite my jail administration project as a Drupal module. Though I wouldn't recommend running this project in a production environment, it's very useful for development environments. I use different jails to keep different development projects organized.