Rituals are spells that require more than one participant (usually 3 participants), similar to Meeting Stones. Current rituals include:
Warlock's 
[Ritual of Summoning] -- Summon a non-present party member to the warlock's location.
Warlock's 
[Ritual of Doom] -- Sacrifices a random participant to summon a Doomguard.
Warlock's 
[Ritual of Souls] -- Creates a Soulwell, containing Master Healthstones.
Mage's 
[Ritual of Refreshment] -- Creates a Refreshment Table, containing Conjured Manna Biscuits.