Book of the Dead (Warcraft III)

Summons 4 Skeleton Warriors and 4 Skeleton Archers to fight for you.

Lasts 120 seconds.

Skeletons summoned this way do not benefit from upgrades.

Source
Arthas can find one in Into the Realm Eternal, chapter 3 of the Warcraft III undead campaign, Path of the Damned.

Warcraft RPG
This ancient, musty tome is decorated with inlaid bones from various creatures. The cover and spine are made from dried skin stretched and treated to remain flexible. The ink used to write the magical words and runes inside is blood drawn from the veins of living creatures killed as sacrifices when the book was completed.