#1 - The Google Office -  http://www.google.com/google-d-s/tour1.html

Contains all the required applications that both professionals and students seek, Google Docs, Spreadsheets and Calendar provides everything for free, online, and accessible wherever you are.

• Google Docs – create, store and share text based documents
• Google Spreadsheets - create, store and share spreadsheet documents
• Google Calendar – organize and set reminders on a calendar that can be synced up with multiple sources including Outlook and mobile devices. 

#2 - Zoho - http://zoho.com/

Zoho is a well rounded online office productivity suite of applications.  The office suite includes these free online applications:

• Zoho Writer – online word processor with spell check
• Zoho Sheet – spreadsheets that can be created and shared
• Zoho Show – create, edit and publish presentations
• Zoho Meeting – share desktops, hold online meetings and web conferences
• Zoho Notebook – create and collaborate on content
• Zoho Planner – organize and maintain to-do's, reminders and notes

#3 - OpenOffice - http://www.openoffice.org

Open Office is a free powerful office suite of desktop applications.  It includes everything you could possibly need to get your work done straight from your desktop:

• Writer - a text editing platform
• Impress - for multimedia presentations
• Calc - for spreadsheets
• Draw - graphics package
• Base - for manipulating database data
• Math - for performing mathematical equations