Doors can be unlocked to allow enemies and prisoners to pass by (only races that have inteligence "humanlike" or above). Note: In order to unlock/lock door, colonist must "flick" the door. Unflicked door will work as unchanged for enemies and prisoners.
Doors can exclude visitors (wanna lock some traders?).
Pet doors for small animals can now be added to doors.
Doors can be assigned to colonists (you can simply restrict rooms to specific colonists without allowed area manager).
New Flicking job: Locking/unlocking doors, it has higher priority than normal flicking job. ("Flicking" doors is needed).
How to use
Select door and left click "Lock" command if you want to unlock/lock door. Right click for more options. Alternatively you can use "Lock" inspector tab.