A module that prohibits you, even as logged in admin, to change the configuration. This is used to protect production sites against unintentional overwriting of settings.
As a teacher, this also has the advantage that I can open sites for the students, who can view all configurations without (unintentionally) being able to make changes to them. You still are able to add content. If you don't want this, you need to set permissions to a new account.
You will receive this message above each configuration form:
Indeed, the buttons are not active anymore at the bottom.
After installation of the module you have to set this in your settings.php. From then on the read-only is active. Remove it, or set it not active, to put it back to the normal situation.