Username Rules for New Registrations
Requires new usernames to be a sensible length, use only letters, numbers, dots, dashes and underscores, and not be just a number.
Snippet Library
Users snippets for WordPress
Snippets for user accounts, roles and profiles: extra profile fields, new columns in the users list, last-login tracking and tighter control of what each role can do. Handy for membership sites, client sites and teams with many authors.