Spellshard

From Eberron: Rising From the Last War, page 279; and Wayfinder's Guide to Eberron, page 116.

Description
Wondrous item, common.

This polished Eberron dragonshard fits in the hand and stores information similar to a book. The shard can hold the equivalent of one book that's no more than 320 pages long. When this shard is created, the creator can set a passphrase and must be spoken to access the information stored within.

While holding the shard, you can use an action to open your mind to the shard, seeing its content in your mind. On subsequent rounds, reading the text or scribing new text on blank "pages" in the shard requires concentration (as if concentrating on a spell) and takes the same amount of time it takes you to read and write normally. Thinking of a particular phrase or topic draws you to the first section in the shard that addresses it.

A wizard can use a spellshard as a spellbook, with the usual cost in gold and time to "scribe" a spell into the shard.

Wayfinder's Guide to Eberron
Consult your DM before using this version. It is usually considered unofficial and invalid due to updated material.

A spellshard is a polished Eberron dragonshard, sized to fit into the palm of a hand. The shard is imbued with a particular work of literature. By holding the shard and concentrating, you can see its pages in your mind's eye. Thinking of a particular phrase or topic will draw you to the first section that addresses it, and a simple ritual allows you to add content to the shard.

A wizard can use a spellshard instead of a spellbook; the spellshard costs 1 gp per "page" in the shard, and otherwise functions as a mundane spellbook. Spellshards can also be used as diaries or journals. More advanced (and uncommon) shards can require a particular mental passphrase to access the contents of the shard.