HR Leave Application system

I find it hard to accept that an IT company with so many tech-savvy employees, would stick to a paper-based leave application system.But , such is the case at my firm.I have taken-upon myself to computerize the system for the benefit of both staff & the environment.And following the precepts of Fred Brooks I will:

1. Steer clear of re-inventing the wheel
2. get it FREE

The office currently uses Google Calender to track which employees are on leave & for what period.However this method:

• Requires double data-entry
• Employee fills-out form
• HR Staff validates request and inputs to Gcalender
• prone to human-error
  
• Paper-intensive

I'm looking into using Google Calender's API in conjunction with Cake PHP provide a solution to our HR woes.