Smeagol is a small wiki engine which uses an extended Markdown as its text format and Git as its persistence and versioning layer.
It supports user authentication against and encrypted password file, and users may be set as administrators (who may add or delete user), but there is no more sophisticated authorisation model.
Only logged in users may edit pages; any logged in user may edit any page. All changes are committed to Git with the username of the author of the change as part of the commit message.