Openoffice is a Free Open source office productivity suit. There are 6 application in the Openoffice productivity suit. You will find that these applications will be more than enough for most office situations.
This is the word processor application. Writes books, letter, documents
This is the Spread sheet application. Does calculation. Small data bases.
Data is a base application. Keeps track of invertories, people and places.
All these applications can do much much more as well.
Openoffice is a Free Open source office suite of applications. MS Office is a commercial suite of applications.