So, one of the ideas I liked from 4e was ritual spells; spells that could be cast, not with spell slots, but with time and money (representing various herbs, potions, incenses, and other sacrifices that you use to enact magic outside of the norm.
Like 4e multiclassing, I wanted to introduce this to TD&D (TSR D&D, separate from WD&D, which is Wizards D&D1), so I've played around with this for a while, finally working it into its current form.
Ritual Casting
Ritual Casting allows a character to cast certain spells, without
memorization, by enacting long and expensive rituals. Not all spells may
be cast as rituals, and each ritual must be individually learned, and
recorded as if in a spellbook. As might be expected, higher-level
rituals are difficult to come by. A character's chance to learn a ritual
is equal to their chance to learn spells based on their intelligence
(in RC, where spell learning is automatic, this is not necessary).
Rituals learned do not count against a magic-user or similar character's
maximum number of spells known.
A ritual has a minimum casting time of one turn per level squared; this
is added to the casting time of the spell. Rituals also require 100
silver pieces per level squared, in addition to any required material
components. If the ritual involved is clerical in nature, then
characters who are not priests of an associated deity increase the level
by 2. This penalty can be reduced by 1 if the character has some reason
that they would know rituals associated with such a deity (eg a Paladin
or Ranger, or a character who has been portrayed as devout). An
"associated deity" is one whose priests are capable of casting the spell
(a more significant factor in 2nd edition).
Rituals are cast at 1/2 the character's level (round down, minimum 1),
unless the spell is one the character would be able to cast based on
class, at which case they are cast at full level, even if the character
themselves is not currently able to cast those spells; for example, a
3rd level Cleric would cast Remove Curse at 3rd level, despite them not
being able to cast that spell until 5th or 6th level. A 3rd level
fighter or thief casting the same ritual would only function at level 1.
Paladins and Rangers may cast spells available to them at full level,
even before they are spellcasters, but RC Fighters are not Paladins or
Avengers until they reach the appropriate level. A character of any level can cast any ritual they learn; a 0th level
character might cast Gate, provided they have access to the ritual, and
to 8100 silver pieces worth of materials.
Many NPCs who sell spells prefer to use rituals where possible; it means they do not have to memorize the spell that day, and they can always charge their client for any expended ritual and spell components.
Learning Ritual Magic
Ritual Casting is a skill available to all characters.
Rules Cyclopedia: General Skill, Intelligence Based, requires the
Alternate Magic skill, and sufficient intelligence to be literate. Skill
in Ceremony can reduce the non-cleric penalty by 1.
1e: Determined by DM; if NWP are not in use, may require a secondary skill. Requires character to be literate.
2e: Ritual Magic is an Intelligence-based skill in the Wizard and Priest
groups, requiring two slots. Characters must also be literate.
Proficiency in Religion can reduce the non-cleric penalty by 1.