Mordenkainen's Tome of Flows

Wondrous item, legendary (requires attunement by a bard)

A large, leather bound tome, each page filled with rhymes, poems, songs, and jokes, written during Mordenkainen's brief, but strong, artsy phase. This tome has 3 charges, and regains all expended charges daily at dawn

While attuned to this tome, you may choose to exchange any of your spells known for another spell on your spell list, when you finish a long rest. If you choose to exchange a spell you gained from your Magical Secrets feature, then you may take the replacement spell from any spell list.

Also, whenever you expend one of your Bardic Inspiration die, you may spend 1 charge and recite an entry from the tome. If you do so, the creature that uses that die may choose to add the maximum result instead.