Without doubt OpenOffice is the best free office program pack that exists.
It comprises a text processor (Word compatible), a calculation sheet (Excel compatible) and a presentation program (PowerPoint compatible). Its interface is also very similar to the well-known MS Office (that so many people use) but with the advantage that it`s free. If you are one of those who use Microsoft Office (or you have to give your work to those that do), and you don`t want to lose your work, you won`t have any problems, because as we have said, all its formats are compatible.
With this program you can do almost any job you like, and you have at your disposal many tools to make life easier (the best known and the best of the least well-known of MS Office). It also allows you to move your files directly to PDF or the useful XML language.
As you will see, it occupies very little disk space compared to its power, and thanks to its excellent installer you won`t have any problems to start using it.