Pixel is the game library (API), which Open Eggbert is built on.
API
Pixel is set of Java interfaces and several classes.
To use the Pixel Game Library, you have to use a backend (or implement a new one), which implements these interfaces.
Backends
Scene 2D
Scene 2D features are located in the package com.pixelgamelibrary.api.scene2d.
Pixel Scene 2D is inspired by LibGDX Scene 2D.