sentences:  The book "Programming Linux Games" covers a couple of the available APIs suited for video game development for Linux, while "The Linux Programming Interface" covers the Linux kernel interfaces in much greater detail.Beside majority of the software which acts as an interface to various subsystems of the operating system, there is also software which can be simply described as middleware.A multitude of companies exist worldwide, whose main or only product is software that is meant to be licensed and integrated into a game engine.