Once Upon a Time is a card-driven storytelling game for 2-6 players. It runs about 15-30 minutes and can be easily played by children with basic vocabulary (about age 7 and up). For more information, see the game page on Board Game Geek. You can also watch Wil Wheaton showcase the game on Tabletop.
Each player is given a secret card with a specific ending written on it. The object of the game is to play all the story cards in your hand and finish by revealing your ending card and tying up the story according to the ending on it.
This game has few rules, and the rules it does have are loose. Generally, one player at a time is the storyteller. As the storyteller, your goal is to narrate the story using the story cards in your hand. Each story card depicts a character, thing, place, event, or aspect. The trick is you can’t ramble too long without playing a card, but you also can’t play meaningless cards just to empty your hand. The game doesn’t give any hard lines or clear definitions for these boundaries; your table has to handle it as you play.
If you can’t think of a way to use any more cards in your hand or you simply have writer’s block, you must end your turn as the storyteller by drawing a card and discarding another from your hand. This helps get rid of cards that seem impossible to work in. The player to your left then picks up the story where you left off.
This game has another mechanic called interrupts, which are exactly what they sound like and exactly as derailing as you expect. If the storyteller mentions something that’s depicted on a card in your hand, you can hijack the story by playing the card and assuming the role of storyteller. There are also special interrupt cards that can be played any time someone plays a story card that matches the interrupt card’s type. Just to kick you while you’re down, if you get interrupted, you must also draw a card.
This game is excellent for helping children flex their young, creative muscles. It builds vocabulary, critical thinking, and a bit of public speaking. It also painfully builds patience. For younger (or immature) players who may get frustrated by being interrupted, it might be best to play without interrupts.
Once Upon a Time is a great creative exercise but may be a turn-off for more competitive players or those who don’t like ambiguous rules.