A Network Operating System (NOS) is a computer operating system purposed to govern and assist workstations, personal computers and servers usually connected to a Local Area Network. A example of this would be, Microsoft’s LAN Manager.

LAN Manager is a network operating system by Microsoft which functions as a server application. This system is run by Microsoft OS/2, and was developed in conjunction with 3Com (Amongst the largest networking companies in the world).
Another function of this network, is that it provides great multi-tasking capabilities as it supports a great majority of desktop operating systems such as DOS, OS/2 and Windows Clients.