Here's two snippets from the introduction of Legends of Ardeas: Orcs,
along with a less formal, and rather lengthier discussion of the main
design philosophy.

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WHAT IS LEGENDS OF ARDEAS

Legends of Ardeas is an RPG set in a detailed fantasy setting, featuring
a wide variety of races, each with a rich background and specialized
rules. This book you hold in your hands contains everything you need to
know to play, and all the information about one of the world's races,
the orcs.

All you need to play is this rule book, some pencils and paper, and
several sets of polyhedral dice, which can be found at your local game
and hobby store.

Naturally, this book is fully compatible with all other Ardeas books.
While one book is all you need to play the game, collecting several will
allow you to mix and match characters and settings for a more epic game.

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HOW DOES ARDEAS DIFFER FROM THE AVERAGE RPG?

The typical RPG features a single core rule book, containing the
absolute bare essentials needed to play. These rules are perfectly
functional, but tend to be somewhat sketchy and lacking in details.
Therefore, the creators release a seemingly endless series of source
books, each expanding and detailing another aspect of the game. A source
book with better rules for magic, one with an extended list of
equipment, one for each continent of the world, etc. etc. To create a
single character, or run a single campaign using the full rules for
everything you plan to include, you may need dozens of these source
books handy.

Ardeas is structured somewhat differently. Each race in the game has a
self-contained source book, containing all the detailed rules one would
normally have to buy a dozen source books for. Detailed special rules
and histories, unique classes and equipment, and maps of every part of
the world that the race is found in.

This sort of division also makes each race something more than a short
set of stat modifications. While in other games, orcs are simply a big
dumb race that makes good fighters, here orcs have a wide variety of
viable classes to chose from, each with a uniquely orcish flavor.

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To put it more bluntly, take a look at the core rules to your favorite
RPG. Lately, with nearly all of them, that's not even one book anymore,
it's going to be at least 2, likely 3. You have the Player's Rules,
which ultimately boil down to how to create a character, and a list of
skills/spells, maybe some flavor, likely the basic rules. Then you have
the GM's Rules, with any basic rules not covered in the Player's rules,
some general GMing tips, some sample adventures maybe. Then if it's an
issue, odds are good that The Big Book'o'Monsters is yet another book
you can't really get started without. Some games go with an all in one
core book, but even then, it tends to be either all there's ever going
to be, or down the line you get that first Companion book with all the
important rules they left out.

Plus in all these cases, to continue the line, we get books which go
into way more detail on pretty much everything. Here's the expanded
spell list and some better mage rules. Here's the rules for handling
vehicles. Here's something that makes fighters actually playable. Here's
a new campaign setting with 3 alternate races, some maps, some monsters,
and a boatload of flavor text. Here's another Companion book to clear up
some of the vagueries in the big books of spells, vehicles, and
equipment.

I don't like this breakdown very much. I know it's not an intentional
thing designed to bleed money from my pockets (at least, not usually).
You're starting with the basics and adding the advanced stuff in later.
All well and good from a certain point of view, but it sucks when I hit
that highly advanced point! For a single campaign, with a specific tone,
I need (or at least want) to have on hand: All the core rule books, the
improved race rules for all my PCs, the improved class rules for all my
PCs, the rules for the setting I'm using, and possibly a couple extra
books for some of the more interesting NPCs. That's 10 books, easy. Or a
massive pile of notes copied out of them.

So here's the Ardeas approach. I take the level of detail I'd have with
all those specialization books, and throw it all in from the start.
There's no way I could fit this in a single book with a nearly realistic
page count, so I break it down along other lines. Specifically, I break
it down region by region, and race by race.

My default campaign world here doesn't have the big ubiquitous
civilization, incorporating every race that has enough intelligence and
manners to do so can be found hanging out in the lobby of the same inn.
It's more like J.R.R. Tolkien has things set up, where the dwarves hole
up in their mountains, the elves stick to their forests, they each have
their own unique culture and values, and if you see one of them in a
city built by the other, that's going to come as a surprise.

The first benefit of this setup is that if you're going to be running
your whole campaign in, say, the part of the world inhabited by humans,
with an all human party (likely, as mixed race parties are only likely
to come up if there's some sort of major, whole world needs to unite or
we're all doomed sort of situation), then you will flat out only need
one book for that whole campaign. Character classes? There's 20 or so.
Skills? Plenty, and I even say what happens when you fumble. Flavor?
Plenty. Maps? Dozens. Historical info to suggest some adventure hooks?
Got'em. Monsters? An ecology's worth. Stats on other races? Plenty to
get by. Rules for having that one token elf in the party raised by
humans? Everything you need to know. Weird specialized rules for massive
wars? They're in there. The only reason you would need another book is
if the campaign became a world sweeping affair.

It's the second benefit though that I really like. Each book covers one
race, with the assumption that all the PCs are going to be members of it
in a typical campaign. Therefore, races have some seriously original
flavor.

Take your basic Generic Fantasy RPG. I want to play an orc. I get, say,
+2 Strength, +1 Constitution, -2 Intelligence, and -1 Wisdom to reflect
my big dumb orciness. I'd make a terrible mage, the best I can get in my
primary stat would be 4 points lower than that of a really great mage
from a race who's good with such things. If the GM is planning a nasty
campaign with no room for whimsical characters like the stupid mage or
the clumsy thief, I'm pretty much stuck being a fighter.

Now look at Ardeas Orcs. Here, every fighter is an orc. Every mage is an
orc. Heck, the 5 year old daughter of the local blacksmith who was
stolen in the night by Big Evil Things is an orc. If I used a basic
class list across the board, campaigns played with this book would have
no mages, or terrible ones at least.

Therefore, I don't have a common class list. If you're an orc (or at
least, raised in orcish society) you only deal with the orcish class
list. Are orcs still big and dumb? Yeah. More suited to fighting than
nerdy stuff? Yeah. They are orcs after all. So I set up their culture
that way. With orcs, you aren't a fighter. You're a big crazy brute
who's an expert at a certain style of combat. There's a class just for
people who want to specialize in using an axe the average person
couldn't lift. There's a class that's all about finding huge monsters
and riding them into battle. You want to be more of the dexterous limber
sort of fighter? There's even a class you could arguably call an orcish
martial art. It mostly involves a lot of running on all fours and biting
people but it's in there. Meanwhile, the mages? There's a special system
of orcish magic designed not to rely so much on studying books and such.
It's mainly about watching mages from other races cast their spells, and
doing your best to copy them. You don't end up with some high refined
art, but the meat and potatoes of tossing fireballs and boosting armor
ratings you've got down pat.

Every possible angle is totally valid for every single race, and with
this system, you can take two characters from two different races,
running with pretty much the exact same character concept, look at them
side by side, and see that they work in totally different ways, with not
much skill overlap at all. This same mentality extends to the sort of
equipment different races have, their economies, social structures, a
lot of custom rules for each race, and so forth. It makes them all
unique, rather than just a collection of different physical features and
stat modifiers.

The disadvantages to this system? Well, for one thing, I need to write a
dozen or so thick books at once to make sure each has enough info on its
neighbors that you only need multiple books if you're going full tilt
with multiple races. For another, the whole thing's a tad sink or swim.
The rules are simple enough that any roleplaying vet should pick it all
up in no time, but this is a terrible system to cut your teeth on. For
me though, this isn't a problem, as the RPGs I design are pretty much
targeted towards people who want a change of pace from what's out there.
Other games can cover the front door, I'm happy in the back room.