Windows NT 3.51 comes in two different forms, Windows NT Workstation and Windows NT Server, which were released in May of 1995. Both are the same operating system, however licensing and packaging are different.
Windows NT Server gives more priority to server processes, uses a licensing agent, and comes bundled with additional server software programs.
Windows NT Workstation gives user applications more priority and limits the number of simultaneous network connections to 10 users.
Windows NT 4.0 Workstation and Server became the successors of Windows NT 3.51 in July of 1996.
later; Microsoft continued to support 3.51
until 31 December 2001.