What kind of software does a business office need? Most businesses deal with documents; they create, modify, and print them. They also perform some calculations, starting from simply recording expenses to maintaining more sophisticated spreadsheets full of stock exchange information. Businesses often require to keep track of inventory, likely in the form of a database with a user interface. Oh, they send e-mails, tons of e-mails. They send e-mails to their customers and business partners, and they exchange documents within the organization. The employees spend a lot of time in meetings, so they need some software to track and schedule meetings. In these meetings, they do presentations.
If you make a list of essential office software, you will inevitably list a document processor, spreadsheet/tables software, a simple database-management system, e-mail client... sounds familiar? That's what Microsoft Office provides.