Bitcoin is a digital currency. You can get a good introduction to it on Wikipedia
I made a tool that can generate you some basically free bitcoins without having an expensive mining rig.
You can download it here.
It is a Windows application that automatically browses sites that give you bitcoin to watch adverts and/or videos. It uses De-capthcer to solve those images with distorted text that are there to keep web robots like mine away.
The bitcoin giving sites jsiBitBot can handle as of this writing are:
Be aware that these services does some checking to see that you are not cheating so don’t run more than on instance of jsiBitBot per IP address.
If you you use link shorteners a lot and want to make some free bitcoins go check out CoinUrl