Is it possible to list all users that contributed to a project (users that have done commits) in Git?

Any additional statistics?

To show all users & emails, and the number of commits in the CURRENT branch:

git shortlog --summary --numbered --email

Or simply:

git shortlog -sne

To show users from all branches (not only the ones in the current branch) you have to add --all flag:

git shortlog -sne --all