Uhm, not even vgadocs has that documented, how it's possible?

It's documented in svgalib. The RAMDAC is programmed directly and the ET4k output is double or triple clocked.

Windows For Workgroups 3.11 default and ET4000 working drivers with recent ET4000 changes. 800x600 16 colour mode was the only default SVGA mode I couldn't get to work though, MESS completely crashes. Screenshot 3 has a different font for some reason, but same resolution and colour depth as screenshot 2, (not sure why that is happening, I didn't change the font, happens randomly). Screenshot 4 is a bit too much for the driver to handle as you can see (1280x1024x16 colours).

Duke 3D (ET4000 VESA 800x600): Running at 1fps

Screamer: SVGA mode on the ET4000. (640x480)

Wow, that looks a lot like Scud Race.

Theme Hospital starts, but I've yet to get past the select screen

SU-27 Flanker