From QuakeWorld Wiki
NPRQuake is, at its core, Win32 GLQuake. The drawing guts have been ripped out and placed in a number of Dynamic-Linked Libraries, but everything else has remained pristine and very true-to-Quake. Additional functionality was added to accomodate for our ripping of the drawing stuff, but none of the additions affect gameplay in any way.
 Sketchy NPR
The sketchyNPR attempts to simulate a person rapidly sketching the Quake environment on a piece of white paper. The walls are shaded with a hash-style sketching, and the water ripples with every stroke of the writing utensil.
 Blueprint NPR
The blueprintNPR attempts to simulate blueprint-style designs people create before constructing buildings. The walls, water, and everything else is left without shading, as blueprints are classically constructed for quick access to dimensions - not three-dimensionality.
 Brushstroke NPR
The brushStrokeNPR attempts to simulate a person drawing each line in space with a brush of your choice. Whether it be a ballpoint pen or a scribbly charcoal pencil, the brushstroker is a work of pure artistic class.