DirectQ is a port of Quake to native Direct3D 9. The primary focus is on replicating the original look and feel of software Quake, but it also has significant usability and rendering improvements.
The old Quake engine was hardware accelerated using OpenGL. However, it was written in the infancy of OpenGL (at a time when even texture objects were only available as an extension), and several of the rendering methods used back then had some room for improvement. Furthermore, it is known to cause issues with some manufacturer's OpenGL drivers. Rather than hacking around at the existing codebase, I felt that a clean start was preferable, so that I could implement better and more modern practices from the outset rather than have to deal with legacy baggage.
There are a lot of people who have business class laptops which have integrated graphics adapters on them but which can't run Quake. These people deserve better than Solitaire and Mah-Jong.