VLT machine

i developed the slot game i have to know how to implement this in which OS
And how to custom the os
how to interface it with external devise

You don’t provide details, but consider starting with a Raspberry Pi based setup. The hardware is ideal for an inexpensive but very capable breadboard environment. Both the hardware and operating system have many, many choices for customization. Use whatever programming language you want. There is a large and very active community supporting Raspberry Pi projects.

Hi,
iam using unity to built the game ,
i need to know hoe to install in os ,
while booting it has to open directly to game ,and the controller (external peripherals ) to work with it

There's now a Linux build of Unity 2017.3, with a new installer for Linux. The linked page was published over a year ago. You again do not specify what OS you are using. The web pages for Unity and whatever operating system you are using are far better sources of how-to-do-it articles than this forum.