OpenOffice.org is an open source office suite, that can be freely downloaded. The suite is available for Linux, Windows, Mac OS X, Solaris and FreeBSD in over 170 different languages.
OpenOffice.org began life as a commercial product called StarOffice, produced by Star Division. When Sun Microsystems bought the German company in 1999 they decided to make the program open source. There are several major variants of OpenOffice.org, expamles being StarOffice (Sun's enhanced version), OpenOffice.org Novell Edition, and NeoOffice (an Aqua native port for Apple OS X).
OpenOffice.org's native file format is the OpenDocument Format (ODF) an international standard (ISO 26300).
Writer is a word processing application that is, in principal, much like Microsoft Word. Writer works natively with it's own file format, OpenDocument, but has the ability to work with Word (.doc) files as well as giving the option to export to HTML or Portable Document Format (PDF).
Writer encorporates the standard text editing tools alongside a spellcheck enabled dictionary, autocomplete, style sheets, tables (also known as TextFrames), indexing and bibliographical tools as well as illustration and image insertion tools.
Writer supports exporting documents to an email client directly.
Spreadsheet application similar to Microsoft Excel.
Presentation application similar to Microsoft PowerPoint.
Vector Graphic and drawing application
Mathematical Equation Editor