Cool! I was actually just looking for a tool like this a couple of weeks ago. I stumbled across git-cal[1], which only works on one repository at a time, but it doesn't require you to import your commits first like this one does[2].

Here's my output from both tools, generated from the repo I spend most of my time in at work: http://i.imgur.com/chrmeP6.png.

[1] https://github.com/k4rthik/git-cal

[2] https://github.com/IonicaBizau/git-stats#importing-and-delet...

EDIT: Just noticed that the "contributions" counts differ.

    peterjmag@peters-imac ~/checkouts/rg/community (git::master) 
    $ git rev-list HEAD --author="Peter" --since="1 year ago" --count
    1205

But git-stats shows 1292. What does it count as a contribution?