Unlike Internet, intranet connections only work in a small place. This can be an organization, a town or some close towns. It does not need a server.
Intranet applications usually include a sort of e-mail and similar services. LAN messenger is an example of intranet communication application.
It offers personal and group messaging. Since it is sometimes used to share professional secrets, it is really beneficial that one can encript messages.
Messages appear on desktop and recipients can be notified with an alert that is a part of this application. If they miss something anyway, they can read it later as everything is saved.
With proper regulation and reasonable usage, such platforms can be beneficial. They are practical tools to coordinate and to share things.