Grim Tales Spellcasting:
Grim Tales expands the d20 Modern concept of the six base classes (Strong, Fast, Tough, Dedicated, Smart, Charismatic) to 20 levels. There is no specific class of spellcasters. Anyone with at least one rank in Spellcraft may potentially learn a spell (provided he finds it somewhere) and thus cast it.
Casting a spell requires to succeed a caster level check (d20 roll) against a DC = 10 + spell level. In casting a spell the caster saps his lifeforce and suffer 1d6 point of Constitution temporary damage, for every level of the spell cast. Spell is cast at the character's caster level (here zero) or the level of the spell, whichever is better.
Three of the classes have access to the Magical Adept talent. This gives the character a caster level of 1, but more important, gives him "Spell-burn resistance" equal to his Intelligence or Wisdom modifier (whether if arcane or divine magic) that his applied to each d6 of "spell burn damage". Note that a natural 1 cannot be reduced. Then, remaining spell burn is substracted from Strength rather than Constitution.
As all ability damage, loss is recovered at the rate of 1 point per night of sleep.