JP Software is a small company whose most important product had been 4DOS, written by Rex Conn in 1986-2004, and released first as shareware in 1989. They have also written other shells: 4NT, 4OS2 and Take Command. Now their flagship product is 4NT. Because its sales have been greatly reduced, 4DOS was released as freeware in 2004. A couple of years later, its source code was released too. Now, its development continues as a free and open source program - see http://4dos.hit.bg where new builds with source code patches are offered. 4DOS is still the most powerful command interpreter for DOS.