Alternate Reality: The City
If you have images enabled in your browser, you should see a screenshot above. It is taken from the original Atari 800 version of the game (I did not take it myself, I found it on the web). This is the intro and not representative for gameplay, but it shows well the for an 8-bit platform astonishingly high quality of the graphics.
Alternate Reality: The City featured a fantasy/SF mix, a single hero instead of a party (uncommon for its time, though by many not necessarily considered an advantage), a moral alignment that is not predefined (as in Dungeons & Dragons) but developed through actions (as, more than a decade later, in the Fallout games). Ported to most platforms of its time, it can be considered a true classic.
This list is by no means complete, but the more important versions should be covered. At some point Phillip Price started, but never finished, a Windows remake.
If you want to play Alternate Reality: The City on a PC, you can either try to play the DOS version, which should run best on a 286 or 386; or, better, the Atari 800 version in an emulator, for which you'll probably need a Pentium.
If I were forced to choose a "best game" on the 8-bit, I personally would nominate AR as one of the best games of all time on the Atari. With splendid graphics, stunning music, and innovative game play, and add the fact that it’s a game that will have you wanting more, AR has it all for a role playing game. I'm only hoping Phillip Price could finish his Alternate Reality sequel.
