In a campaign where magic is limited, you may want more variation in classes than the standard fighter and thief will provide. A deceptively simple way of handling this is through adapting spells as special abilities ("Techniques").
Each character elects 2 first level spells that he can utilize as a technique. Techniques are assumed to be non-magical in nature, instead representing unique, innate or trained abilities the character has managed to master.
Techniques are powered by Energy. A first level character has 2 points of Energy, effectively permitting each technique to be used once, or one technique to be used twice.
Energy is restored at a rate of 1 point per 4 hours of sleep or 8 hours of regular activity.
Characters receive an additional point of energy at levels 3,6,9, 12,15,18 and 20.
Characters acquire additional techniques at levels 4,8,12,16 and 20.
The energy cost of a technique is 1 energy per level. Spells that are strictly non-combat and have no outside effect (such as detect evil) can be reduced 1 level.
Spells can be of any source.
Any level dependent spell is cast at level 2 ability.
In game-play, techniques must be explained as non magical sources,and may have additional limitations based on their implementation. For example "Magic Missile" would represent a masterly archer or knife thrower, while "shield" would be a unique defensive maneuver. "Protection from evil" may be from a holy man's iron faith or a shaman's war paints.
Players and DM's should feel open to interpreting and extrapolating as the situation warrants.
Some spells may not be usable at all.
Example: My character is a witch hunter, who hunts down heretics and their demonic allies. I pick "cure light wounds" and "detect magic", renaming them into "first aid" and "sense of the otherworld".
In discussing with my DM, we agree that using the first aid ability takes a few rounds to perform, so it's not usable in a battle. Sensing the otherworld works in a general area around the character, roughly one room indoors and will pick out magic (including monsters in Fantasy Europe)
Example: Two heroes both elect "fireball" as a technique. The first hero is a tinkerer type, and rationalizes the ability as a chemical compound that can be hurled. The second is a viking who rationalizes it as a berserk rage, allowing him to strike every enemy in a melee.
Creative and cool? Crazy and broken? Let me know what you think, and if you can test this in a game.