Get the list of contributors for repository:
git log --format='%aN' | sort -u
Display addition/deletion statistics per author:
git log --shortstat --author="Marcin Olichwirowicz" | grep -E "fil(e|es) changed" | awk '{files+=$1; inserted+=$4; deleted+=$6} END {print "files changed: ", files, "lines inserted: ", inserted, "lines deleted: ", deleted }'
You can filter it by adding --until or --since
git log --shortstat --author="Marcin Olichwirowicz" --since="1 Jan, 2013" | grep...
If you want just a number of commits, you can use:
git shortlog -sn