The demand is such that the niche has grown from text-based games coded by hobbyists to between 30 and 50 professional audio-game developers who sell 3,000 games a year, experts estimate.

Most of these games run on ordinary PCs and are often joystick- or keyboard-controlled. The player dons a pair of headphones, and elements of the game are delivered in stereo to help players shoot aliens on the left or avoid a tank on the right. —David Cohn —The Blind Fragging the Blind  (Wired)