FBUI

Framebuffer UI (FBUI) is an in-kernel windowing system for Linux (kernel version 2.6.9 only, currently outdated) that sits on top of the framebuffer subsystem. Unlike the X Window System, FBUI consumes very little memory: the entire subsystem is about 50 kilobytes. FBUI supports features expected of modern windowing systems, such as moveable overlapping windows, multiple windows per application, events and common drawing functions, as well as windows on every virtual console. Graphics operations are executed on a first-come, first-served basis inside the kernel, and there is no server that queues requests.

Included with FBUI is libfbui, which provides abstractions for windows, events, images, fonts, etc., as well as quite a few sample programs such as load monitor, clock, calculator, scribble pad, image viewer, window managers, and a simple MPEG2 player.

FBUI, being only 50 kilobytes, offers solid proof that a windowing system need not be several megabytes in size, as is the case with X Window System.

FBUI is primarily intended to be a 2D graphics system, although it does include a triangle-fill routine.

>>5
Protip: OS X is a Unix, and Aqua is not part of its kernel. Windows did indeed make the GUI part of the kernel up until Vista, and that decision single-handedly created its reputation as an extremely unstable OS. There's a good reason Vista divorced the GUI from the kernel.
X may be a mess, but this is would only make things worse. And also you're an ignorant buffoon.