Realm started out as an engine alpha by mh. 
He since moved over to working with cplusplus and using direct3d instead of opengl.
I picked up the engine and over the years i made several improvements.
Heres a small list.

Pk3 support (commpressed pk3 also).
ARB shaders (water/heathaze etc.).
Much improved VM (game logic) by bengt jardrup.
Safe print buffers.
Vertex shaded light.
Bloom.
Mod support (xm sound files mp3 etc.) uses midas which is now open source.
Drawlump (nehahra uses this) Realm does not play nehahra yet though.
Video menu for setting custom resolutions (Realm by default renders in your monitors max resolution).

Things the engine had from the start but modified a bit.
Dot3 bumpmapping on surfs (generated internally expanded to take external textures as well).
Caustics.
Underwater fog.
Detail texturing (uses math not a texture actually).
Skyspheres.
Vertex Arrays (only on renderer when i first got it expanded to everything).
Fake specular.
Luma texture support (expanded to also take glow textures).
Per content shading of liquid surfs (modified quite a bit over time).
Stencil haze on lava surfs.
Stainmaps.
Better particles.
Better lightmaps.

TODO.
Bumpmapping on alias models.
Remaining bugs (can crash on some special games/maps) most notably bastion of the underworld.

Realm does not need any external content to run besides the id1 folder but i have included a pak with lits for id1
+ a few other things. If you want to have the best looking game get the textures from q1 retexturing project.

And lastly. 
Realm needs a pretty recent gfx card (dont try and run it on your laptop unless you have one with anything else than an intel gfx chip).
Cards from nvidia 6600 and up should run it just fine older models should work also but might be slow.

Happy fragging :)

