Well, I had this idea for a while now...
My idea would basically mean there are no ''spells''. Instead, it would combine several ''incantations'' into a defined power.
Example:
We combine three variables; Type Shape Intensivity
For type we could say Fire or Heal or Cold or Acid ...
Shape could define how it appears, like Projectile or Ray or Splash ... Ex.: Fire Projectile would be Fire Arrow while Fire Splash would be a Fireball.
Intensivity would simply mean how much magical energies the caster invests into the incantation. The more the better. Of course, only high-skilled spellcasters would be able to reliably cast the more intense ones. Novice casters would get various ''fun'' effects.
Anyway, this was just a quick show. There could be different variables and so on, I don't know how it would all be done.
Where was I? Oh ... at the start, you would have only a few incantation choices available, like only Fire, or only Ray etc. As the caster gets more skill, gets them from another source (books, scrolls, as apprentice at another wizard?) and then (if played in Fort Mode) *add learned ones to the Fortress's shared knowledge.
* That is, if they'd have a shared knowledge. Could be more fun if each caster would have his own pool of incantations.
Or maybe each guild, group etc.
Hopefully you understood me, though not likely. I just wrote down the crap in my head.