These customized applications are written by and for end users, not by software vendors. This can get tricky, because some value-added resellers and system integrators write such customized programs to sell. The difference is they are not selling generic applications software as Microsoft, Borland and Lotus do. They, like the end-users themselves, are creating customized programs using the software of developers such as Borland and Microsoft. This presents some complications and indicates some changing directions for the PC network industry.
Networks exist for applications.
That is, users install networks to get a job done. Users can have computers, cable, interface cards, file servers, and protocols, but without applications software users can't do much but copy files from disk to disk. Network application software is what people use. The network is just the substrate upon which they use it. Network-ignorant applications are written for use on one computer by one person.