Splatbooks are historically thin (64-96 pages) and relatively inexpensive. Most splatbooks will contain 3-5 chapters: a history of the splat, a description of the splat as it exists in the current setting, relations between the splat and other splats, game rules covering new splat abilities, a selection of sample starting characters for the splat, and notable examples of the splat. Most splatbooks had an introduction written in a consistent style across the splat (i.e., Werewolf: The Apocalypse intros were always comics, while Wraith: The Oblivion intros were all segments of a larger story). More specific details are given below:
World of Darkness
Between the first editions of Vampire: The Masquerade and Werewolf: The Apocalypse, the first edition of Mummy was released; this sub-line, arguably the ancestor of all fatsplats, underwent another revision (adapting afterlife rules to fit with Wraith: The Oblivion) before being superseded by the hardcover fatsplat Mummy: The Resurrection.
Additionally, Kindred of the East was meant primarily to work with Vampire, but was quite capable of meshing with other World of Darkness core rulebooks, as was the Middle Kingdom fatsplat Demon Hunter X.
Vampire: The Masquerade
First and Second Edition Vampire used one series of clanbooks, with a new set of revised clanbooks coming out after the revised edition. The Vampire clanbooks are as close to a generic splat as possible. V20 saw the release of a single-volume sourcebook, Lore of the Clans, which adapted as much material as possible from the revised clanbooks to the V20 ruleset.
Werewolf: The Apocalypse
Werewolf: The Apocalypse had two classes of splatbooks over its history. There were Tribebooks for each of the thirteen Garou tribes, following the same release pattern as Vampire. In addition, Werewolf had a series of Breedbooks, which covered the rest of the Fera. The Breedbooks were generally thicker and more detailed than the Tribebooks, with the exception of the second Breedbook that covered the Nuwisha; the third book (covering the Corax) explains the reasons for this in a "Word from the White Wolf Game Studio":
- Alright, already! We get the hint!
- For those of you who bought Nuwisha and wondered why it was so slim compared to Bastet, well, that was the plan. In fact, the original plan was to put out the Changing Breed books, one and all, as 72-page mock Tribebooks. After all, you didn't want the repeated material from the Players Guide, right? Bastet would be the exception to this rule, simply because there are nine tribes of them – impossible to cream into 72 pages. Everything else would be slimmed down to avoid that "repeated information" bugbear.
- Well, popular demand said otherwise, and so here you go. Corax, and all successive Changing Breed Books, will be whatever size we figure is necessary to give you whatever rules you need to generate an appropriately fleshed out character, along with the detailed history and culture sections you've grown to love. Big and fat, just like you asked.
- Happy now?
Mage: The Ascension
Mage: The Ascension published Tradition books in the same fashion as Vampire and Werewolf. In addition, a set of Convention books were published for first and second edition. These Convention books were unique among splat books in that they had no playable characters. Following the publication of the Guide to the Technocracy, a revised Iteration X convention book was released, but no further Convention books were revised until 2012.
Wraith: The Oblivion
Wraith: The Oblivion published an incomplete line of Guild books through its history. These guildbooks were initially published as single guild books, but later releases were thicker, two-guild books. The guildbook line ended before covering all guilds, with the Mnemoi and Ferrymen covered in Ends of Empire.
Changeling: The Dreaming
For Changeling: The Dreaming there were seven Kithbooks released, covering seven from nine Kiths. The Sidhe kith was detailed in Nobles: The Shining Host and in the three Books of Houses, each covering a different set of Noble Houses. The only kith to never get a Kithbook were the Boggans.
Kindred of the East
Hunter: The Reckoning
Hunter: The Reckoning did a series of hunter books covering the various creeds (including the "lost" creeds of Deviance and Isolation introduced in the Hunter Players Guide). There was also a series of enemy books covering the various monsters of the world from an Imbued perspective.
Vampire: The Dark Ages
Vampire: The Dark Ages produced three clanbooks: Clanbook: Salubri, Clanbook: Cappadocian, and Clanbook: Baali. Notably, none of these were actually clans during the modern VTM era; the Cappadocians were usurped by the Giovanni after the Dark Medieval, the Salubri had already been usurped by the Tremere, and the Baali were never a clan, only a bloodline. In addition, four larger splatbooks called Libellus Sanguinis covered the other twelve clans (four per volume) and their history up to the 1197 CE.
Dark Ages: Vampire did not publish clan-specific splatbooks (clans were covered in the player's guides to the High and Low Clans), but did publish a set of Road-specific splatbooks covering the five major Roads. The Dark Ages line also introduced the first fatsplats with the Dark Ages: Inquisitor, Dark Ages: Fae, Dark Ages: Werewolf, Dark Ages: Mage and Devil's Due supplements.
The splatbook-equivalents for Trinity were sourcebooks, each covering a given psi order as well as the region of the Trinity Universe in which it has its base of operations (America Offline, for instance, covered Orgotek and the FSA).
Exalted had two types of splatbook lines: fatsplats for the different types of Exalts (with the core rulebook covering the Solars) and for the Fair Folk, and standard splatbooks for the Solar castes and the aspects of the Dragon Blooded. The Aspect Books are distinctive for having a sequence of unusually potent Dragon-Blooded fully detailed in the characters section (as opposed to just having starting characters). These Dragon-Blooded were intended to be used in advanced campaigns or as antagonists in a Solar-centered campaign.
Only Exalted First Edition saw splatbooks for the sub-splats. New versions of all of the sourcebooks for the fatsplats and the Fair Folk were released for Exalted Second Edition, and fatsplat sourcebooks are likewise planned for Exalted Third Edition as well.
Chronicles of Darkness / New World of Darkness
For the most part, Chronicles of Darkness, also known as the New World of Darkness, had "splatbooks" covering an entire axis of splats (the "inherent" splats or the "social" splats). Vampire: The Requiem received individual hardcovers (like all World of Darkness books), each about 200 pages long, for each covenant and, later, each clan, covering what it means for members of each clan to pass their Requiems in that splat. The supplements on the orders of Mage: The Awakening follow a similar structure, detailing what it means to be a member of a particular order. However, the Paths were covered collectively in Tome of the Watchtowers instead of receiving individual splatbooks. Werewolf: The Forsaken did not receive any splatbooks for individual splats. Instead, Werewolf: The Forsaken received two books that covered an entire class of splats: Tribes of the Moon covered the tribes, and Signs of the Moon covered the auspices.
Of the games that came after the "big three", none received any individual splatbooks, but several instead had a single supplement that focuses on splats (usually in addition to some other topics). The Promethean: The Created sourcebook Strange Alchemies focuses on the Bestowments and Refinements. Likewise, the Changeling: The Lost sourcebook Winter Masques focuses on Seemings as Kiths. Hunter: The Vigil received a splatbook, Compacts & Conspiracies, which covered the titular Compacts and Conspiracies as a whole; the book was serialized online, with each splat available individually or as part of the full book. Geist: The Sin-Eaters received no supplements at all, save for supplementary material in World of Darkness: Book of the Dead.
It is perhaps worth mentioning that each of the three games has a series of anthology supplements on examples of the smallest subsplat in the game: bloodlines for Vampire, lodges for Werewolf, and legacies for Mage. World of Darkness: Mirrors, the Mage Chroniclers Guide, and the Vampire: The Requiem sourcebook Danse Macabre all present optional and expanded systems for new and existing splats.