OD&D does this really well with Fighters. Your Fighter can be a knight, or a pirate, or a robin hood, depending on how you outfit and play them. Nice.
The new wave of the OSR has provided us with several adaptations that turn the Thief into a Specialist or Expert or Adventurer, which creates a similar effect: you have a class that provides non-combat skills, be it a box-man, architect, diplomat, tracker, whatever. I like it.
But spell casters are not so flexible. The spell list contains enough flavor and world-implication that your Magic User is always a D&D Magic User, and your Cleric always tithes to the Church of Gygax.
|Gustav Doré, Don Quixote, 1863|
I present a completely flavor-drained spell list. Just straight mechanics. Want a Fire Mage or Shadow Walker or Time Lord or Gadgeteer or whatever? Just pick the mechanics you need and dress them up in lovely fluff.
It's a lot easier than writing out a whole new spell list, and I think it can be a fun part of character creation. The best part of superhero rpgs is rolling up a random assortment of powers and then trying to figure out how they fit together, right? This is like that.
Boring Spells for the OSR (a pdf)
A few notes:
This formulation of Boring Spells is intended to be OSR multi-edition compliant. It assumes standard level advancement and Vancian magic. I actually started down this road while reworking my AES Microlite20 variant. I'll share that version, in which I take more liberties, in a bit.
There are spells that create diseases and poisons. I left out any descriptions of how these work, since there is such a variance between editions on these matters. If you don't have a favorite mechanic, just assign a saving throw, roll d6 for damage (or Attribute Loss if you're nasty), and repeat every day until the character is cured or dead.
Stripping the spells down like this, it's a lot easier to compare apples to apples, and see which mechanics belong at different levels. Feel free to add your own spells (or to adopt stripped-down version of other spells you find out there), and just plug them into whatever level seems appropriate.
There are exactly 100 Boring Spells. Handy for randomly determining what's on a random scroll, or in an NPC's spell book. The d100 version of the spell list will be in the Microlite20 post.
This doesn't address any other class differences you may want to use to separate out your Clerics from your Witches and whatnot. It's just a bunch of Boring Spells.
Edit: Here some examples: Some Boring Spell-Casters.