Rental cars need to be transported between offices. And travellers love freebies. Combine the two, and you get free rental cars, organized by Transfercar. The New Zealand startup works with major car rental companies including Europcar, Apollo and Ace. Each rental company has a host of 'relocation cars' that need to transported to different branches. These are listed on Transfercar's website, along with the dates they're available, and interested customers can book online after registering with Transfercar. Drivers can also request to be notified by text message when cars are available for routes they'd like to travel. Most vehicles include…