sentences:  This version was instead based on OpenDOS 7.01.xx.DR-DOS 8.1 was withdrawn for GPL violations (see Controversies).Aside from selling copies of the operating system, the DRDOS, Inc. website lists a buyout option for DR-DOS; the asking price is 
  
  The OpenDOS 7.01 source code was a base for "The DR-DOS/OpenDOS Enhancement Project", set up in July 2002 in an attempt to bring the functionality of DR-DOS up to parity with modern PC non-Windows operating systems.