There are several free alternatives but by far the most ppoular (and which is used by many schools, police forces, local authorities and health authorities) is Apache OpenOffice:
http://www.openoffice.org/
Many AB members (including me) use a recommend it.
The major commercial alternative to Microsoft Office used to be the Lotus software sold by IBM. When IBM decided to no longer compete with Microsoft, they generously placed their software into the public domain. It's now know as IBM Lotus Symphony, and completely free. If, for some reason, you don't like Apache OpenOffice, it might well be worth a look:
http://ibm-lotus-symphony.en.softonic.com/
Chris