You might have missed if you were rushing through the game or ignored anything that wasn't pertinent to your quests at the time, but Fallout 3 has a playable text adventure in one of the terminals at Hubris Comics's office. Titled Reign of Grelok (beta), the mini game doesn't offer any rewards for completion, but it's a neat homage to Infocom-style text-based adventure titles.

As pointed out by soon-to-be-closed Insert Credit, programmer Chris Marjason recreated the game in Flash, mimicking the terminal interface but allowing you to just click options instead of typing commands (He also seems to have fixed one of the beta's glitches). Now, anyone can with a browser can play Reign of Grelok (beta)!