OpenOffice.org has been until recently the leading open-source office software suite for word processing, spreadsheets, presentations, graphics, databases and more. It is still a great choice but has been superseded by LibréOffice as the leading Office Software.
LibréOffice is a fork of OpenOffice that occurred after OpenOffice was obtained by Oracle when it purchased Sun. Many developers did not like the way that Oracle was handling OpenOffice so, because OpenOffice is Open Source code, they simply took the last available code base, renamed it, and started a new course of development form that point.
OpenOffice is available in many languages and works on all common computers. It stores all your data in an international open standard format and can also read and write files from other common office software packages. It can be downloaded and used completely free of charge for any purpose.
A large amount of free OpenOffice documentation can be found here: http://documentation.openoffice.org/. Most of this documentation is available as complete documents or as individual chapters, all in PDF format.