Invented by Elliot Rudell in 1982. It was once marketed as "Scrabble UpWords". You start off by playing words just as in Scrabble, but then you can change words by stacking new letters to form new words. The play grid of 8x8 is much smaller than scrabble and the scoring system favors stacked words.
Tim:
I like it. It's also the only scrabble like game I'll play. Given the way the scoring favors changing existing words it actually gives me a chance to win even if my spelling might "need some work".
Laura:
After decades of playing (and usually winning) Scrabble, UpWords feels like the same game, but isn't at all. Despite the fact that I'm quite good at word games, I've managed to lose each game against Tim. The biggest differences are 1) the game play - you have to shift your thinking from just 'playing a word' to 'playing a word that can be easily changed with other letters' and 2) remembering that the game board is rather small, so it is more difficult to place new words down. It's a fun and challenging game. I'll play this again, at least until I win!