New action history was released on 23.10.2018!
All organizations can view logs of changes to users, report exports, contacts and absences by accessing Action history from top navigation.
Organizations using Action history add-on (Enterprise version) can in addition view changes made to projects and invoices.
Action history logs specific actions and those are displayed with the date and time the change occurred, what was changed and the person who changed it.
Check out the support article related to Action history for more detailed info.