The Tobii Interaction Library makes it easy to use gaze for interaction! It also provides robust, built-in eye tracker connection management and easy access to standard data streams, all in a lightweight library.
For interaction, in general you want to know if the user is looking at an object (eg a button or game object) rather than at a certain coordinate. This is often called gaze to object mapping. The idea is that you provide the Interaction Library with information on where your interactable elements are (called Interactors in the API), and the library will provide gaze focus events. The Interaction Library makes the focus determination using advanced algorithms that take into account raw data noise, gaze offset errors, physiological and gaze behavioral eye/gaze effects, relative object sizes and z order, and more. This results in smart and stable object focus events without sluggishness and jitter.
The Interaction Library is available for Windows (32-bit & 64-bit), MacOS (64-bit) and Linux 64-bit) and ships with support for C++, C and C#.