For a long time i had accepted the concept of the Knowstones as normal. A Knowstone is basically knowledge of how to cast a spell embedded into a stone. Knowstones can be used by spontaneous casters like Sorcerers, Bards, Assassins, Rogues and Shadow Dancers to get more spells in their repetoire than their maximum allows.
Surprisingly there was no standard to be found in existing 3.5 books for Knowstones that i found satisfactory. Thus i am making my own system for them. There are now many more Spontaneous caster classes then before, so Knowstones are more relevant then ever. The price of a Knowstone is basically 500 x (caster level x spell level).
Equipment PDF has been updated.