We all agree that spammers don't use spaces in their usernames, right? This module forces users to use spaces in their usernames so that spammers can't register (until they figure out a way to). With the 7-x.1.1 version, you can now specify your own character and how many times this character should occur in the username.
#D8CX: I pledge that Spaces Enforced! will have a full Drupal 8 release on the day that Drupal 8 is released.