Forgotten code, VGA600
Low resolution graphics modes like 320×200 are displayed with doublescan so that each logical line is drawn twice, that way 320×200 is drawn with 400 lines which looks better than 200 on a modern CRT monitor. The reason is that modern CRT monitors are designed to be able to display 1000 or more lines and if they are feeded with just 200 there would be huge black bars between these thin 200 lines, with 400 lines its better but still not good.
VGA600 is a little DOS TSR which i wrote in 1996/1997 to solve this problem, VGA600 does that by monitoring the state of various vga registers and if it detects that the current graphic or text mode can be improved then it improves it by increasing the number of lines and dot clock. So for example 320×200 would be displayed with 600 or 800 lines (which it is depends on the configuration)
Source code under GPL, README and binary are available too
Ive extensively tested VGA600 with doom and quake with a ET4000 PCI card a long time ago ;)
Patches welcome, especially ones porting this to linux and modern vga cards :)