DR DOS (or DR-DOS) is an OS, a free-for-non-commercial-use version of DOS; was once released as OpenDOS, but Caldera reverted to the historical name. Caldera Systems, Inc. (now SCO, they acquired it and subsequently reverted the company name to SCO) does no more own it.

It's basically the very stable and complete implementation of DOS by Digital Research, built off CP/M-86 (see a little known history of why Novell bought it "Digital Research - The Untold Story", by Marc Perkel), with some networking and multitasking capability, ROMability, etc. Sources for the kernel have been released, but the free software community that gathered around that event (OpenDOS FAQ by Alaric B. Williams here and there) felt betrayed because Caldera did not make the system free of rights, and did not release all the sources after all. Go FreeDOS instead!

Caldera also sue the well known Seattle-based company for unfair competition practice in forcing people and vendors not to buy from competitors, at the time DR-DOS was technologically way ahead.

This page is linked from: DOS