Allows moderators to view a history of edits to a message.
Copy the extension to phpBB/ext/towen/editlog
Go to "ACP" > "Customise" > "Extensions" and enable the "Post Edit Log" extension.
If you can't see the Editions log link under a message that you know has been edited, check to ensure that your user account has the 'Can see the edit log' moderator permission.