BuddyPress.org

Yeah, it seems to work fine by replacing the three lines of the username block with mt_rand. However be sure that there are letters somewhere in the value, such as the “mem” above. Buddypress will throw back an error without letters.

Also this probably wouldn’t work with large websites with thousands of people, as the chance of generating the same username goes up. You’d probably have to write a function that generates a long string of random letters and numbers.