Can Stack Exchange prevent users from signing up with a username that is already in use?
33449
Why does Stack Overflow allow duplicate display names?
125255
How to ensure that all new users have the same profile settings as the current user?
85575
How to prevent user registration
30157
How do I hide a particular user from the login screen?
45973
Can I prevent/restrict standard users from installing/uninstalling software?
81286
Allow "Save And Copy Profile To All Stack Exchange Accounts" to exclude selected sites
22176
Keep short history of user display names
149252
Is it possible to separate professional Stack Exchange accounts from personal ones?
56949
Want to prevent a user to access other user cases
45436
How to stop instagram app remembering / auto-filling in username at login screen, when not yet logged in
147553
Should unregistered users be prevented from posting questions on Stack Overflow?
19126
Old usernames stick to Community Wiki posts
84748
The user name remains displayed when selecting another site (tablet device only)
45016
Allow registered users to hide username when asking privacy-sensitive question
58071
How to safely change username and hostname?
125941
Prevent users from starting multiple accounts?
58116
Argument for/against splitting login process into checking username, then ask password?