A car rental software is used by pure car rental companies like Avis. The software helps such companies to setup a rental management system and manage all the cars that have been rented out. It also has features for fleet management etc. Most car rental companies provide cars that needs to be self driven by the renter.
A vehicle hire software is used mainly by Taxi dispatch companies. These companies provide cab, taxi on hire for passengers. The duration of the hire can be anywhere between 15 minutes to 2 hours on an average. Innovative companies like UBER, LYFT etc. have taken the standards of vehicle hire software to next level. Most vehicle hire companies provide cars that have a driver driving it for you.