A cute little git command to quickly see where the activity has been when exploring a large codebase:

$ for d in $(find . -mindepth 1 -maxdepth 1 -type d | grep -v .git)
> do
> echo -n "$d,"
> git log --oneline --since=30.days $d | wc -l
> done

This will give you output like:


From this point its trivial to visualise it as a pie-chart or some other mechanism.