wp-block-admin

It's simple and still working(2016).

The code for this plugin is very simple which explains why it hasn't needed an update for several years. So far I've installed it on one site and no problems yet. It's a great solution for those sites where the user profile is provided by our front-end and in some cases the username/password are synced from an external source, or depend on external values and therefore can't be modified.