Google Docs and Spreadsheets
As the name applies, Google Docs & Spreadsheets (D&S) is an online word processing and spreadsheet application and is a replacement for Microsoft Word and Excel. Google provides online storage so that all files can be accessed through any computer totally eliminating the need for a desktop computer. Furthermore it supports MS Word and Excel documents that can be uploaded without any problems (complicated documents with extensive tables, graphics may see some formatting alterations).
MS Word and excel documents received in Gmail can be opened directly in D&S eliminating the need for MS Office to be installed on the local computer.
D&S supports extensive collaborative features including the ability to allow simultaneous real time editing by multiple users. For e.g. a number of people can edit the same document at the same time and everyone will see the changes made by others in real time. This makes it very useful for writing academic papers.
Video demonstrating the usefulness of Online collaboration
Google has also recently released an online powerpoint application also (see example presentation).
Google docs and spreadsheets tour
Video Tutorial:
Besides google there a number of other websites providing similar applications. Notable among them include:
1. Zoho office
2. Think Free online