nVidia Optimus support for Linux through VirtualGL - dkms
This project contains bumblebee (formerly known as prime-ng) and was initiated by Martin Juhl.
Bumblebee is Optimus "support" for Linux with real offloading.
It uses two X servers with a software solution (VirtualGL) to transfer the nVidia graphics to the Intel GPU.
It works on Optimus laptops without a graphical multiplexer.
You have to use the nVidia drivers from the Bumblebee-Project for the best performance: