Just to update everybody, don't use ftp.gmd.de anymore. The site is no longer being maintained and all its content is now at ftp://ftp.ifarchive.org and is being maintained. Apparently, the gmd site was supposed to be shut down because the place was being bought out or some such, and everybody decided to move to the US. As for the original Infocom games, the best place to get them is to find a used copy of the Masterpieces of Infocom CD. This CD contained the vast majority of the games, but is getting really hard to find. I managed to pick it up a few years ago from an online store that featured hard-to-find software. There is a web site http://infodoc.plover.net which has the documentation for some of the Infocom games in text format, and most are in PDF. The eventual goal of the site is to provide documentation for all the games in both formats with the text version containing descriptions of the graphical content, but it still has a ways to go. In many of the Infocom games, the documentation is absolutely necessary as they used it as a form of copy protection. As for the Frotz interpreter, I've found that the Linux version is usable, but doesn't read very well with speech. It tends to repeat itself when the screen scrolls. Games written with Tads and using the Tadsr interpreter seem to read better, but both are playable and provide great entertainment in Linux. Another great place to check out Interactive Fiction as they like to call it plus some other stuff is the Chungkuo BBS. Just telnet to chungkuo.org and apply for an account. The only thing required is a valid email address so they can mail you a randomly generated password and they say that they delete the address after that. You can find Infocom games, many rare text games, a lot of old BBS doors, and board games on the BBS. It runs Linux too, so that makes it a perfect showcase of the power of Linux. when you can play LORD with other players logged in and then go to an Infocom classic or play Checkers against the computer (Braille display recommended if you have it,) it really is a testimony to how powerful a PC running Linux is compared to one running Windows.
