http://mariadb.org/
Basically, it is similar to MySQL, but I think it should be supported, since the distro's might end up switching over to MariaDB instead of MySQL. This is probably due to Oracle owning MySQL.
If Yii supports it, you'll be able to use it.
That is good to hear. I'm sure it will, since it will be binary compatible with MySQL. It uses XtraDB, which is their equivalent to InnoDB.
And it looks like Yii does from a cursory google search.
I could probably make a MariaDB driver for mybb 1.6 for you to use.
From what i've seen it's compatible with MySQL functions in PHP, so wouldn't mybb work on it fine anyways? maybe im just confused :\ lol
MyBB works on MariaDB fine (as it's just a drop-in MySQL replacement).
You can even use the Aria storage engine instead of MyISAM without issues.
I've been running my forum on MariaDB + Aria storage engine for quite some time already.