users

This gives you a single box where you can enter tokens to form the default username.

It seems to work, but in D7 the patterns section ("Only use the below pattern elements") was empty. This is supposedly because there's a dependency on the 'profile' module, except profile doesn't exist in D7 (I tried profile2 instead but it made no difference) and profile2 doesn't exist in D8.

auto_username displays tokens OK and is more powerful / has more settings including customise at what point names are truncated, etc.

D7 only (as this is in D8 core as standard).

Converts /admin/people into a fully-fledged configurable view (i.e. fields, filters, exposed filters, header/footer, pagination settings etc.) 

(Dependency: views_bulk_operations)

Use tokens to merge first name, last name or any other fields.
Then you can display the realname field in various places.  

Note: you have to add code to substitute the default username in the title of user node views - e.g. in mytheme_preprocess_block(&$variables)

Ordinarily, if you grant a user "Administer Users", they can do everything *except* change the roles (they don't even see the checkboxes).  You could give them 'Administer Permissions', but that also allows them to do other things.  

This module lets you set which roles they are allowed to enable for a user.  Administrators still see the roles checkboxes in the usual place (below 'status' on /user/123/edit), but everyone  gets a new 'Roles' tab.  

Works with D8 but not updated since April 2016.

Patches:

I'm not using any patches, but there are a couple RTBC-ed  the queue.