What currency requirements exist specifically for Commercial and ATP pilots that a Private pilot wouldn't know about?
Autoland currency

If equipped with autoland, the flight crew will have some requirement to use the system, or else autoland operation in real CAT III weather, where autoland is required, will be prohibited. For many types, this also applies to the aircraft itself.

Currency is satisfied by conducting a successful autoland in any weather, so in periods of good conditions, autolands may be practiced during normal CAT I or CAT II approaches. Crews can also do this in the simulator. All autoland use is reported to the company so they can track currency.

It varies by airline policy and aircraft type, but typical requirements may be one every 30 days, one every 90 days, or 2 or 3 landings between 6 month sim checks.

Some airlines will put a movable placard on the flight deck as a reminder to crews what the status of the aircraft is, e.g. you will see "CAT II" or "NO AUTOLAND" when the system is faulty or not current.