DirectFB is a radical new way of running graphical applications on a Linux machine with acceleration.
It is actually a thin library that provides hardware graphics acceleration, input device handling and abstraction, an integrated windowing system with support for translucent windows, and multiple display layers on top of the Linux framebuffer device. You need to at least have the 2.4.x kernel Framebuffer installed in order to use DirectFB. There are several demo programs included in the package to give you an idea of what it can do.
This is not actually an X server, but it is an alternative to one.