Background time tracking application

I've a bad memory, therefore I can't recall where I spent my time during last day, last week and definitely not last month. However I still need to log my hours and generate reports to track the projects evolutions and time spent in each feature. Ok, nothing new so far. Problem is I used [ManicTime](http://www.manictime.com/) and I loved, it silently collected all my info day after day and when I had to check where I spent my hours in certain day, I simply check by hour by day and it was perfect. But on mac... I found a huge list of application that or doesn't do a proper tracking (harvest, timings, tyme) or doesn't give me reports I want like RescueTime. Is there any application that silently does the job? As I work with multiple virtual machines, cross platform support is a big plus.