World of Farland
The World of Farland is a fan-made Campaign Setting for Dungeons & Dragons and Pathfinder that has been around for over 18 years, having spanned every edition from 3.5 through 4e to 5e. Whilst it began as an online project, and still can be found online, it has recently begun selling its work in hardcover physical books through the website DriveThruRPG, with these books boasting new content exclusive to them and never seen on the webpage before.
Setting Lore
As a setting, the World of Farland is characterized as a Dark Fantasy, taking your standard Heroic Fantasy world and adding elements of both Lord of the Rings and A Song of Ice and Fire. Similarly to Midnight, or arguably to 4e Dark Sun, Farland presents players with a world conquered by evil for many long years, but where hope has recently dared to rear its head. Most of the world is ruled over by one of seven Lords of Sin, powerful sin-fueled champions of the dark god Vornoth, but a rebellion has broken out and freed several once-conquered kingdoms in the West. Whilst these points of light are teetering on the brink of collapse, and an all-out war against the dark powers is looming, the players are heroes who have a chance to tip the balance in the favor of the Light.
There is also a spin-off "prequel" setting called War of Immortals, which is set in the distant past of Farland and presents a world where the great elf and dwarf civilizations battle against the orcs and goblinoids of Stor-Gris, whilst humans and halflings are but simple tribal folk, still huddling in caves.
Splatbooks
There are currently five splatbooks for the World of Farland; the Campaign Setting, the Player's Guide, the Dungeon Master's Guide, War of Immortals, and Realms Under Shadow.
The Campaign Setting is, of course, a strictly lore-centric splatbook that examins the setting as a whole. Everything from racial lore to geography, climate, detailed cities and towns, cultural notes, the local pantheons, campaign advice, etcetera.
The Player's Guide is all about PC-focused material; new races, new class options, new backgrounds, etc.
The Dungeon Master's Guide provides new DM-centric lore and mechanics for the Farland setting, such as new monsters and an outline of the setting's cosmology.
War of Immortals contains lore and even some mechanical stuff relating to this "prequel" setting, including new PC races and new monsters.
Finally, Realms Under Shadow expands the overall world of the Farland setting by examining its equivalents to Asia, Africa and India, with lots of new races, class options, monsters, gods and other such goodies to make running campaigns in these lands or crossing them over with the "core" lands possible.