Made for a Kickstarter reward.
Constellation Games is a serial novel by Leonard Richardson, who you might know as the writer of the excellent short story Mallory, or the designer of robotfindskitten. It involves a man whose first instinct when the space aliens arrive is to wonder what kind of videogames they play. Gatekeeper is one of them.
The best way to explain it would be to quote the chapter at you, but basically you're in charge of making sure people transition correctly from the land of the living to the land of the dead, and vice versa. (Ghosts with Serious Business to attend to are allowed to return briefly; but if it's the living half of a dead Farang demanding a refund, flick them back from whence they came.)
Played with the mouse, rather than the inscrutable abacus/pipe organ controller that the Brain Embryo originally shipped with.