It was originally developed by Bernie Roehl and Dave Stampe back in 1991, and has been the basis for several VR-related books (notably Virtual Reality Creations).
REND386 is available for free on the Internet, and is included with Virtual Reality Creations and several other popular books.
In late 1993, Bernie and Dave decided to go their separate ways. Bernie went on to create AVRIL, which is a complete rewrite from scratch with a much-improved programmer's interface and backwards compatability for objects and worlds. Dave continued working on REND386, renaming it to VR386 and making several improvements.