You can also get the free LibreOffice which will be a perfectly suitable drop-in replacement for MS Office for the vast majority of people. For that matter, the bundled with Windows WordPad is sufficient for a wide array of people's needs.
OpenOffice is good for free alternatives as well, have never tried libreoffice.
LibreOffice is essentially an offshoot of OpenOffice. When Oracle bought Sun Microsystems, and inherited OpenOffice, there were several months where not much was done in terms of development. This is when LibreOffice was born and picked up where OpenOffice left off. OpenOffice has since resumed development under the stewardship of the Apache Foundation, but it still lags significantly behind LibreOffice.