CHECK constraint not implemented in MySQL, what about other DBMS? MariaDB, which is based on MySQL, does not.
Oracle, including Oracle XE 10g and 11g do.

I'm curious as to other DBMS?
Every R (relational) DBMS I've used has.  MySQL is peculiar in so many ways I struggle to put it head to head with any of the "normal" RDBMS for anything other than a basic data dump for a simple application.

There are plenty of DBs that are not relational that don't have the concept.  As far as I know though, there are none other of either sort that support the syntax without the functionality.