Dvorak Simplified Keyboard
The Dvorak Simplified Keyboard is a keyboard layout designed for the use of English speakers, created by Dr. August Dvorak in 1932. The goals of the layout included reducing fatigue and increasing typing accuracy and speed. Although the ubiquitous QWERTY layout is used by the great majority of typists, the Dvorak layout is the second most popular layout for English-speaking typists.
Dvorak users often promote the layout as a way of improving typing speed and reducing the risk of repetitive strain injury from typing. This is due to various features designed to reduce the amount of movement necessary to type a given word. Dvorak skeptics consider such claims a form of woo. If so, it may at least be a relatively innocuous form, as switching between Dvorak and QWERTY layouts is quick and easy on most computer operating systems, no longer requiring special hardware. The main inconveniences of using Dvorak are the time invested in becoming proficient with that layout, and the potential for confusion when a QWERTY typist and a Dvorak typist use the same computer.
Is it superior?
The issue of whether Dvorak is really better than QWERTY is difficult to settle, in part because the largest and most well-known studies on the matter are contradictory, fairly old, and considered biased (generally by whichever side doesn't agree with a given study). August's original study with the Navy Department showed an increase in typing speed for Dvorak users, but the Navy's follow-up study failed to replicate that result. Large, well-controlled studies are difficult to perform, because the popularity of QWERTY predisposes most people to have more experience and more interest in that layout. Dvorak typists may feel that switching to Dvorak has reduced typing fatigue, but non-anecdotal evidence is hard to come by.
Oddly enough, the Dvorak/QWERTY debate has developed a political aspect. QWERTY has sometimes been used as an example of how an inferior technology can become widely adopted, and thus, used as a counter-example to claims that the free market always results in the best product. Unsurprisingly, this provoked a reaction from a few libertarians.
The choice of keyboard layout, at least between QWERTY and Dvorak (ignoring other possibilities like Colemak) is largely an endian dispute (which is chosen doesn't matter, but a choice must be made) and QWERTY holds on because the effort involved in switching to a layout hardly anyone uses is judged to be a greater inconvenience than the claimed failings of QWERTY.