DOS Plus (also known as DOS+) is an operating system written by Digital Research, first released in 1985. It can be seen as an intermediate step between CP/M-86 and DR-DOS. DOS-Plus would change its name and become DR-DOS in 1988.
DOS Plus 1.0? - Jan 09, 1986
DOS Plus 1.2 - April - July 1986. In July, 1986 GEM was released