Vik Rent Car most important features:

Vehicles Categories (Van, Station Wagon, City Car, etc.)
Vehicles Information (images, details, description)
Vehicles Features (4 Doors, Air Conditioning, Manual, Automatic, etc.)
Vehicles Options Management (GPS, Ski Rack, Baby seat, etc.)
Car Damages and Distinctive Featues for each unit (License Plate, Fuel-in etc..)
Options Pricing (daily price or fixed price to be added to the rental cost)
Pickup and Drop off Locations
Pickup and Drop off Location Fees or Discounts
Vehicles Availability Calendar
Vehicles Availability Search Module (front end)
Tax rates
Types of Price (insurance, kilometers etc. Daily Price, Weekly etc.)
Seasonal Prices (Charges or Discounts to be applied to the standard rental fares)
Special Prices for altering the prices in some days of the year (seasons, holidays, weekends)
Hourly Prices for rentals shorter than 24 hours
Extra Hours of Rental Fees
Out of Working Hours Fees
Online Orders with custom methods of payment
Vehicles Availability Calendar Management from the Admin Panel
Payment Framework that supports custom payment gateways
Paypal Payment Gateway
Other Methods of payment with ssl support (Bank Transfer, Offline Credit Card...)
Payment of the entire amount or order deposit
Customizable Html Order eMail
Invoice and/or Contract in PDF format can be sent by eMail (the PDF is customizable with a template file)
Search Statistics
Bookings Export in CSV format for software like Excel or OpenOffice
Bookings Export in ICS format for calendars like iCalendar, Hotmail, Outlook, Google Calendar etc.
Bookings export in XML format to synchronize the orders with your own client Software.
iCal Live-Sync with any iCal software like Google, Yahoo and many others. 
Multi language Support (Joomfish and FaLang Content elements included)
Orders Overview
Custom Order Fields
Front-End Availability Calendar for Each Vehicle
Google Maps for Locations with markers placed in the given Latitude and Longitude
jQuery UI Datepicker Calendar for the dates selection

VikRentCar is used by a lot of well-known companies for vehicles rentals like Avis, Budget, Hertz, Sixt, Thrifty, Europcar etc...