git-guilt
Show total blame count for files with unstaged changes or calculate the change in blame between two revisions.
TLDR
Show total blame count
$ git guilt
Calculate the change in blame between two revisions
$ git guilt [first_revision] [last_revision]
Show author emails instead of names
$ git guilt --email
Ignore whitespace only changes when attributing blame
$ git guilt --ignore-whitespace
Find blame delta over the last three weeks
$ git guilt 'git log --until="3 weeks ago" --format="%H" -n 1'
Find blame delta over the last three weeks (git 1.8.5+)
$ git guilt @{3.weeks.ago}