In Eureka!, players race to spot a shape on the table that matches the challenge card that's just been revealed: Which shape has two sets of parallel sides? Which has a perimeter less than or equal to seven? Which has three or four obtuse angles?
Each player has three cards in front of them, with these cards having been taken from their personal deck; each one shows a shape against a grid (to help players identify the properties of that shape). If a player chooses the correct shape, that card is discarded, and if that card was in front of an opponent, the active player discards one of their cards as well. If the player chose incorrectly, they put their own card under their personal deck and draw a new one (thus setting themselves back one card); if they chose the opponent's card, then they place that card under their deck, helping their opponent and hurting themselves.
The first player to get rid of all their cards wins.