Single repository:

git log --pretty=format:%cs | cut -b 1-7|sort | uniq -c | add-missing-months  | awk '{print $1}' | spark

Multiple repositories:

for d in */; do cd $d; basename $(pwd); git log --pretty=format:%cs | cut -b 1-7|sort | uniq -c | add-missing-months  | awk '{print $1}' | spark; cd ../; done