Differences between MySQL and MariaDB

• max_user_connections Can be changed online in MySQL. Cannot be changed in MariaDB if value was set to 0.
• PERFORMANCE_SCHEMA is enabled in MySQL 5.6 and 5.7 by default. In MariaDB disabled by default.
• Replication incompatibilities from MariaDB (Master) to MySQL (Slave)
• MariaDB 10.2.0 still contains XtraDB 5.6. So MySQL 5.7 features cannot be used.
• MariaDB 10.2 Window Functions are missing in MySQL 5.7
• SHOW PROCESSLIST has additional column Progress in MariaDB.
• Progress indication in: mysqldump --progress-reports (default on) for MariaDB.
• MariaDB 10.0 on CentOS 7 uses still SysV init script. MySQL 5.6 on CentOS 7 uses SystemD init script.
• binlog_row_image is implemented in MySQL 5.6 and does not exist in MariaDB 10.0.
• MariaDB 10.1 and older (containing XtraDB 5.6) does not provide flexible/general tablespaces yet which where introduced by MySQL 5.7.
• EXPLAIN FOR CONNCECTION does exist in MySQL 5.7 and does not exist in MariaDB 10.1 or 10.2.

Other sources

• Sidegrade (MySQL - MariaDB - Percona Server)
• MariaDB versus MySQL - Features
• Differences Between the MySQL and MariaDB Query Optimizer
• MariaDB versus MySQL - Compatibility