Running small machine without computer

Hi to All,

I'm setting up a row of 4 small desktop
routers. They'll be single purpose machines
to do the same task repeatedly and nothing
else. This will be basically milling grooves
in 1" blocks of plastic that will be no
larger than 5" x 6".

But I don't need 4 computers or want to
swap wiring...I want them all running at
the same time. Load and let run.

Where or what would I look at, as far as some
small single purpose controller for
each machine. It doesn't even need a video
monitor....just push go and let it do it's
job. Is there a small controller that could
be programmed easily with a single gcode
file or maybe a flash drive?

Thanks in advance!
John