This is a slot machine as operated by Veikkaus, which is the state run corporation operating all gambling services in Finland. There are roughly 20 000 slot machines in use in Finland currently. This is interesting on its own, but things get really fun when you look on the inside.
A fair fraction of the insides is taken by machinery that deals with coins. When a coin is inserted in the machine it first goes in the coin acceptor, which is marked with a green box in the image. It detects the type of the coin. Each denomination has its own exit chute. Bad coins are rejected from the machine while sorted coins get passed into coin hoppers (marked in red).
A coin hopper is basically a bowl of coins and a mechanism that is cabable of ejecting coins from it one by one. When you think of slot machines, you are probably thinking of the sound they make when start spitting out tons of coins after a jackpot. Coin hoppers are what create that particular sound. I recommend looking up videos on Youtube if you are interested in mechanical engineering, because the way they work is kind of fascinating.
The slot machine also accepts notes and debit card payments but these are mechanically much simpler and don't take much space. The only thing remaining in the picture is the box marked in yellow. It contains the actual brains of the entire machine.
The contents of the brainThe main system is, much like everything these days, a regular computer. This specific one is a fairly average industrial PC that is running a custom version of Debian. At boot it starts up the game software that is based on a custom version of the Ogre 3D graphics engine. The computer also manages and controls all other hardware in the cabinet, such as the coin hoppers and note acceptor mentioned above, using a custom, self designed controller board. The cabinet housing the device is also custom designed and built.
Thus, surprisingly, at its core a slot machine is roughly the same as a desktop PC running desktop games with a few extra peripherals. This means is that Linux desktop gaming has been mainstream among the general Finnish population for 15 years, which is roughly the amount of time these slot machines have been deployed.
In addition to the games themselves, the development environment is also 100% Linux. As a demonstration, here is a screen shot of a development version of the software running on a developer workstation.