Idle Airport CEO puts you in charge of an airport: passengers arrive, planes fill, and money accumulates. You spend it upgrading plane capacity, speed, check-in times and the services that keep passengers coming back.
It's a proper idle game, which means the money keeps piling up while you're away — you come back to a balance waiting to be claimed and spent on the next upgrade.
Yes — that's the idle mechanic. Profits accumulate while the tab is closed and you claim them when you come back.
Whatever is currently limiting passenger throughput. Early on that's check-in speed; once planes are always full, capacity becomes the constraint.
Yes — a light browser game with nothing to install.