Google Apps. Microsoft Office 365. What are they and why do we care?
Interesting questions. What does every modern office need? A productivity suite to create and edit documents, spreadsheets and presentations. A messaging system, for sending email and enabling chat. A calendaring system, to facilitate time management and shared scheduling. A collaboration system, to corral projects, tasks, data and team members.
The classic solutions consists of the Microsoft Office productivity suite, Exchange Server for email and calendaring, and Sharepoint Server for collaboration. Why would we consider anything else?