OS/2 is a series of computer operating systems, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2", because it was introduced as part of the same generation change release as IBM's " Personal System/2 (PS/2)" line of second-generation personal computers. The first version of OS/2 was released in December 1987 and newer versions were released until December 2001.
OS/2 was intended as a protected mode successor of PC DOS. Notably, basic system calls were modelled after MS-DOS calls; their names even started with "Dos" and it was possible to create "Family Mode" applications: text mode applications that could work on both systems. Because of this heritage, OS/2 shares similarities with Unix, Xenix, and Windows NT in many ways.
IBM discontinued its support for OS/2 on 31 December 2006. Since then, it has been updated, maintained and marketed under the name eComStation. In 2015 it was announced that a new OEM distribution of OS/2 would be released that was to be called ArcaOS.