Lotus Notes is a network application that can be used to share information. It consists of two primary components: the Notes server and the Notes workstation. The Notes server provides access to data, to Notes workstation users, and other Notes servers. Notes users individually connect to a Notes server so they can read and send mail but most importantly, work in shared databases.
Run as far away as you can from Lotus Notes.
We are forced to use it at work for email and database functions. It's a poor attempt at anything it tries to do: Cumbersome to use, doesn't support common HTML protocols, incompatible with other email programs, etc.