I used to work for a company that used Lotus Notes.
It is an email product, but it also allows you to store data like on-line document that can be shared and build complex end-user applications for large companies.
A large organization like the NHS would use Notes to share information amongst many departments.
In Microsoft terms it is like Outlook and Exchange for the e-mail component and Sharepoint for the application development component.
More about sharepoint
http://www.microsoft.com/sharepoint/default.ms px
I think most people nowdays would buy the outlook, exchange and sharepoint solution.