The Demihumans are a collection of races that are physically similar to humans, but are different and usually smaller. Elves and Dwarves traditionally fit in this category, but are treated separately due to their populus nature.
The demihumans were evolutions of the other races. Shapeshifters evolved from humans, kender and halflings from gnomes and dwarves, and quicklings from elves. Each has their own abilites and tendencies, and is outlined here.
Quicklings are very small cousins of elves. They are incredibly quick. The gods, during the godwars, tried to kill a particular race of elves. This band, continually racing ahead of this god, became so small and quick that they were difficult for gods to slay. They are very tough to hit because of their speed. They are amongst the smallest creatures in the land, so they rely on that speed to help them survive. They speak both common and the sylvan tongue.
Kender are small human-like individuals. Their size and appearance and curiosity can leave them mistaken for human children at times. They have a natural ability to 'borrow' things, sometimes, even without their own consciousness directing them. Small, quick their bodies are suprisingly tough. They speak only the common tongue.
Halflings are the most uncommon of adventurers. They prefer many of the comforts of home, but are some of the most aware of their surroundings of any demihuman. Their short stature makes them poor swimmers, but other than this shortcoming, they are excellent thieves. They speak only common.
Shapeshifters are a secretive race, and this quotation may explain why, of sorts: "As time rolled on in the cosmic being of things, creatures began to be borne with less and less distinguishing features. Pasty skin, dull eyes, hairless, no ears... in all other respects seeming Human. One young Lad, Daarg, found that through concentration, he could change the form of his body into other animals. Soon, his knowledge was widespread of what he could do. Other races hunted and killed all of his kind that they could, while which skills person that could sought refuge to keep their heritage alive from extermination. Shapeshifters they would come to be called." -- Elaz Wllrwrysih, sage, ancient of the High Elves.