GURPS Thaumatology is a 4e supplement.
The work contains the best 3rd Edition magic variants and adds many all-new options.
The main chapters cover "What is Magic?", "Minor Spell Variations", "Major Variations", "Material Magic", "Paths and Books", "Flexible Magic", "Magic is Power", and "Games of High Enchantment".
There are also three Appendixes: Magical Modifiers, Alternative Critical Failure Tables, and Spell Prerequisite Counts.
The full extent of each of these chapters can be seen in the free Preview of the work.