This document details what the Tandy Bit does in Infocom games. The information was posted by Jake Wildstrom, and HTMLized and uploaded by Gunther Schmidl.

Hitchhiker's Guide Release 42, 47, 56
VERSION command Adds "Licensed to Tandy Corporation. Version 00.00." This looks like a bug.
Seastalker Release 15 (both), 16, 86
VERSION command Adds "Licensed to Tandy Corporation. Version 00.00.15"
Suspect Release 14
VERSION command Adds "Licensed to Tandy Corporation."
Wishbringer Release 68
VERSION command Adds "Licensed to Tandy Corporation."
The Witness Release 18, 20, 21, 22
"Vandalism is for private dicks, not famous police detectives." The Tandy bit changes "dicks" to "eyes".
When you ASK STILES ABOUT PHONG, he tells you "He seems straight, but I don't really trust slanteyes." 'slanteyes' becomes 'his kind'.
ASK MONICA ABOUT MURDER yields "Isn't it obvious? That bastard Stiles squibbed him off!" 'bastard' becomes 'idiot'.
If before you accuse her you ASK MONICA ABOUT STILES: "That bastard who killed Dad? I'd spit in his face if it was worth the trouble." 'bastard' becomes 'idiot'.
After you accuse her, she'll say "That poor bastard. First he fell in love with Mother, a married woman; then he actually trusted her husband. I don't know what he uses for brains." 'bastard' becomes 'idiot'.
ASK MONICA ABOUT PHONG: "He's a right gee, no matter what some people say about his race." 'race' becomes 'kind'.
Most actions you try to take on Monica result in her saying: "I don't know what game you're playing, Detective, but count me out. If you think I'm just a dumb twist, think again." 'twist' becomes 'twit'.
If a game fails to SAVE (or SUSPEND) it says that "Your story couldn't be suspended. Consult your instruction manual if necessary." Tandy added "or Reference Card" to that phrase.
If you surprise Monica in the workshop, she says "My God, you gave me a start!" The word "God" is removed.
The VERSION command Tandy says "Licensed to Tandy Corporation." This is the only thing to change in version 18.
Somewhere in the game is the phrase "Necrophilia went out with raccoon coats!" Tandyified to "You can't be that desperate!"
"What a pervert!" (for LOOK UP MONICA) Becomes any of a number of randomly selected messages.
Zork 1 Release 23, 25, 26, 28, 30, 75, 76, 78
VERSION command Claims to be "ZORK", not "ZORK I" (except in releases >= 75). Also, adds "Licensed to Tandy Corporation" to version command.
Endgame text Doesn't invite you to play the sequels at the end of the game.
Leaflet "No computer should be without one!" becomes "No TRS-80 should..." (except in releases >= 75).
Zork 2 Release 15, 17, 18, 19, 22, 48
VERSION command Adds "Licensed to Tandy Corporation" to version command.