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/atari800 (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/share/atari800/atari800.cfg (or similar) which you will probably want to copy to your home directory, at some stage, to personalise the settings. 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 :->).