Papers, Please is a game about being an immigration officer in a fictional dystopian country named Arstotzka. It's quite a unique experience and clearly did well for the developer Lucas Pope.
On August 8th it turned 10 years old, and the official site notes it's now sold over 5 million copies. So that's somewhere around 500,000 copies a year. Considering this is from a solo developer, with a really simplistic graphics style it's genuinely very impressive.
More about it:
The communist state of Arstotzka has just ended a 6-year war with neighboring Kolechia and reclaimed its rightful half of the border town, Grestin.
Your job as immigration inspector is to control the flow of people entering the Arstotzkan side of Grestin from Kolechia. Among the throngs of immigrants and visitors looking for work are hidden smugglers, spies, and terrorists.
Using only the documents provided by travelers and the Ministry of Admission's primitive inspect, search, and fingerprint systems you must decide who can enter Arstotzka and who will be turned away or arrested.
Not only that, the developer even made their own little webgame demake named LCD, Please.
Our contributor Samsai took a look at the game in an old episode of the GOL Cast.