Mir - The purpose of Mir is to enable the development of user interfaces shells.
Bootstrap Magic - Create your Bootstrap 4.0 themes easily with magic
Wayland - Wayland is intended as a simpler replacement for X, easier to develop and maintain.
HackerThemes - Bootstrap 4 themes and tools for web developers
DirectFB - DirectFB is a web-based platform that provides you with complete access to a software library that you can use for the acceleration of graphics, handling the input devices, and others for your Linux operating systems.
Bootstrap 4 Cheat Sheet - An interactive Bootstrap 4 cheat sheet