GoogleDocs - http://docs.google.com/
MicrosoftWebApps - http://office.microsoft.com/en-us/web-apps/
ZohoOffice -  https://www.zoho.com/docs
LibreOffice - http://www.libreoffice.org/
SoftMakerFreeOffice - http://www.freeoffice.com/
KingsoftOffice - http://www.kingsoftstore.com/