Now defunct, the website wizards.com/hottub came from the card Urza's Hot Tub printed in Unhinged. Like the card says, you were basically tutoring by discarding one card and searching your library for a card that contains an exact word from the discarded card. This can be any word in the discarded card's name. This website helped you to search through a database for cards with a single word from as many words as you type in. The results were displayed and from there selecting a card took you to the Gatherer, the official Magic: The Gathering card database.
The last expert-level set to be included in the Hot Tub was Betrayers of Kamigawa.