Tunneler runs at an undocumented low-resolution (160x100) 16-color video mode...
OMG! :shock:

What is it?
A split-screen two-player combat game running in an undocumented video mode, 1991, DOS.
I guess the developer didn't like MCGA/EGA/VGA.
Hell, why use a documented 320x200x8 mode or documented 640x480x4 mode, if we can use an undocumented 160x100x4!