Air lockers are one of 3 major types of selectable lockers. (Cable and electric being the other 2 options) Selectable are the best type of lockers IMO because they allow you to engage and disengage the locker depending on the need. Goes from lock to open differential. This helps on road with snow and helps offroad for tight turning. Air lockers engage by a specified amount of air is applied to the carrier. ARB produces the most famous aftermarket air locker but the TJ rubicons did come with air lockers as well....just run at a different PSI.
I have an arb front and rubicon rear in my TJ. The rubicon rear is a little different than other air lockers in that it is a limited slip when not engaged versus a open differential.
Air lockers are expensive to buy and to install. Many will say that a ARB certified place needs to installed.