All of the game mechanics found in this book are Open Game Content (OGC). Most of the material comes from the 3.5 System Reference Document (SRD) which can be found online hosted by various companies and individuals.
For those readers that are unfamiliar with the SRD and OGC, I should probably give some background on them. Back around the year 2000, some different people involved in the role-playing community came up with a revolutionary idea. This idea was to create a ruleset that would be available to everyone and so that different companies could use it and different games could have similar mechanics. Out of this the 3rd SRD was developed and the Open Game License came into being. A few years later the rules were changed slightly to the 3.5 SRD.
During the next several years, there was an explosion of interrelated gaming material from various companies; all based on the 3rd and 3.5 SRD rule sets. As time went on, more companies began coming up with their own unique versions of the rules, and as these rule sets began to become more different from the SRD, the interrelated material decreased. In 2007, the official support of the rule set was abandoned, though some smaller role-playing companies still continued supporting the rule set in decreasing numbers.
So, I imagine some readers are asking themselves, if almost all of the rules in this book are available for free download on the internet in the SRD or if they already own books that contain those rules, why should they purchase this book or switch to the Gauric Myths system. The quick answer is they shouldn’t. First off, there isn’t really a Gauric Myths rule system, the rules for the most part are a direct continuation of the 3.5 rule set. Where the rules are slightly different, I have tried to put in notes so that groups may continue using the 3.5 rule instead if they wish. Second the goal of this project is not to have anyone abandon their current gaming books, but instead to allow people to replace those materials as they become damaged or to help bring new players in to the game who may not be able to access those previous editions.
As for looking at the SRD online, I fully support this, in fact, I often use them myself, there are great resources out there and everyone should take advantage of them. Another goal of this project is to keep the 3.5 SRD game rules alive, not to make money from this. Thus if a group is using the SRD then those rules are still being used and I will be very happy.
Another detail you may notice is a distinction between things like core classes or races and base classes or races. This was done so as to allow players to have an introductory game and stick to the core classes and races; and later they can add other more advanced rules as they become more comfortable with the system.