Tetra is a framework that abstracts away a lot of Unity's rather opinionated coding style and replaces it with my rather opinionated coding style. It also features stand-alone components that can be used outside the rest of the framework. It provides simple, allocation-free solutions for common problems in something approaching idiomatic modern C#.
In short, the goal of Tetra is to no longer have to write using UnityEngine; at the top of your classes.