MariaDB is already a fork of MySQL, and many developers from MySQL now developing MariaDB.

Isn't MariaDB the fork by Monty, the original developer of MySQL who sold it to Sun in the first place, setting off multiple rounds of cashing out?

MySQL AB also required copyright assignment for all contributions, which made it possible for MySQL AB, Sun and now Oracle to have full copyright over it. MySQL AB wasn't above throwing around GPL FUD to scare people into paying for a non-GPL license.

Yes.

Four known forks so far (http://en.wikipedia.org/wiki/MySQL#Forks)