Here is some material for Ars Magica, mainly the 5th edition.

Campaign information
This file contains some information of the new campaign we're starting, including rules about character and covenant creation.

Total calculator
This Excel worksheet contains all the magic totals a magus needs. Just fill in his arts, characteristics and skills. There are two versions, one where you can fill in the Art scores, and another where you fill in the experience points.
The newer experience-based total calculator now includes also slots for talisman (for spells) and lab total bonuses (for Shapes and Materials). It will also calculate the required seasons for a certain lab project of the final, modified effect level.

5th Edition Errata
This is a pdf version of the official errata from Atlas Games' website.

5th Edition Bestiary
Atlas Games published a mundane bestiary shortly after the fifth edition had been published - it had been left out of the main rulebook.

Spell Mastery
This is a compiled list of spell mastery special abilities, taken from various published sourcebooks. At the moment, listed abilities are from the following books:
  • Ars Magica 5th Edition
  • Houses of Hermes: Societates
  • Houses of Hermes: True Lineages

Character sheets
PDF-sheets
Covenant sheets