Ioun Stone
Wondrous item, varies, requires attunement · 2014 rules, SRD 5.1
Orbits your head; type determines the benefit (e.g. Agility +2 Dex, Awareness, Fortitude +2 Con, Protection +1 AC, Regeneration 15 HP/hour, Mastery +1 prof). Rarity by type.
Also in the 2024 rules (SRD 5.2).