As with any open source software, anyone can download MySQL sources, build binaries for some platforms and distribute their own packages. So we have the official ones from Oracle, MariaDB, and Percona - the makers of MySQL and its forks respectively. There are also those distributed with operating systems or that are available for install from their standard repositories. Some people or groups also create packages out of the most recent versions of various software and make them available to the world. Finally, some mash up a vanilla MySQL with various patches creating even more options. What to choose?