Gem Magic

One of the several d20 books I have on my shelves is R.A. Salvatore's Demonwars Campaign Setting book. It's got a neat flavor to it, despite that I've never read the books its based on. Definitely a lower magic setting than traditional D&D, with most hybrid classes only being permitted if they drop their spellcasting abilities, and clerics/druids/wizards/sorcerers being replaced entirely with setting-appropriate casting types based on the indigenous magic system: specially imbued gemstones.

Woo, objectification.

Sexualized cover art aside, I really like the concept of gem magic and the way it has been implemented in this system.  Enough that I would use it, perhaps slightly modified, in my own games, except that as it is I'm already struggling with too many options and magic systems.  I had wanted to make this system less complicated, not more, and having multiple systems of magic and spellcasting does not fit with that goal.

Regarding the setting's system, essentially there are gemstones which are imbued with magic (as well as naturally occurring gemstones that are not imbued, and can't be used to cast spells).  The type of stone determines what type of magic or effects it can produce in the hands of a skilled wielder.  Certain feats permit wielding two or even three stones at once, combining them to produce new effects not possible with only one gemstone.

The setting uses a mana-type system instead of spells-per-day, since you invoke the power of a stone through channeling that mana into/through it, and gem-wielding classes get 1d8 mana per level, with a bonus from their Con modifier.  This still provides a limiter, which is what a spells/day system does, but there is also the secondary limiter of having any magic dependent upon having one of these special gemstones.  There's no learning new spells each level, or scroll scribing giving a wizard a utilitarian edge.  You either have the stone you need, or you don't - leveling just gives you more mana.  Multiple gem wielders, though, can potentially share stones with each other, and I don't think there's any mention of stones breaking or losing their magical properties with use.

Combining it with any other magic system has the potential to make gem magic significantly under-powered, which means if I do want to use it, it may have to be the only magic system available.  Alternatively, I could keep all these systems as options and leave it up to the players as to what gets used.