I had an idea for Magic-Users, for any sort of game at all, but more useful for games which have severely limited spell slots, especially at lower levels. It was specifically designed for the incredible retro-clone Labyrinth Lord, but since it's based off the same sort of idea that oD&D, BECMI D&D, and AD&D were, I'm certain that it can be used for practically any system that uses Vancian magic.