You've found David Firth's Atari 800 emulator which can emulate the
8-bit Atari 800 and XL series of home computers. 

Please refer to /usr/local/share/doc/atari (or equivalent on your
system) for the distribution documents. A man page has also been
installed. The system wide configuration file can be found at
/usr/local/lib/atari/atari800.cfg (or similar) which you will probably
want to copy to your home directory, at some stage, to personalise the
settings.

If you're at all serious about your emulator then you SHOULD check out
these URL's in the order they're written:

  http://cas3.zlin.vutbr.cz/~stehlik/a800.htm
  http://www.signus.demon.co.uk/index.html
  comp.sys.atari.8bit

The ROM's for the Atari computers are, unfortunately, copyright. This
port will attempt to down-load another freeware Atari emulator for DOS
called PC Xformer 2.5 which contains copies of these ROM files. If you
would like to take a further look at XF2.5 you should find it in your
distfiles directory (if it successfully down-loaded :->).