Explore username and registration modules

View Email Registration on Drupal.orgEmail RegistrationCovered by the Drupal security advisory policy (17,333 installs)
Register with email only (no username).

View Mail Login on Drupal.orgMail LoginCovered by the Drupal security advisory policy (14,345 installs)
Login with email and many other features.

View Real Name on Drupal.orgReal NameCovered by the Drupal security advisory policy (9,419 installs)
Use actual name as username.