Most of us use Microsoft Office for writing report, presentation, Maintain Database, Spreed sheets because we get it free with our PC. But one thing you should remember that what we are using it is actually not free, Most of us are using the pirated copy of Microsoft OS & Office (MS word, MS power point, MS Excel, MS access etc) I will show something with this article that we can use Original Office software, that is Strong Alternative of MS office, most important thing is that this software's are completely free.
The details of those software's are mentioned here:
Adobe Buzzword
Website: www.buzzword.com
Uses: Online Only
Write and collaborate on documents anywhere, anytime

and anything else you need to access online or work on with others. It looks and behaves like your normal
desktop word processor, but it operates inside a web browser, so there's no installation required. It's free.
* Create print-perfect documents
* Collaborate with any number of co-authors
* Access your documents from anywhere
* Control versions and keep track of changes
* Useful document dashboard
* Easy image placement
* Flexible lists etc.
Blist
Website: www.blist.com
Uses: Online

Weblist is shortly says Blist. It is the combined of small database that will fulfill all your needs related data.
It is made very simple for new users. You can also use this at your blog or social network page.
Etharpad
Uses: Online
Website: www.etherpad.com

Etherpad is based on Online storage, Sharing text documents that is explained as "Pad". More than one people can work on a text document at the same time.
Evernote
Website: www.evernote.com

Can be use at Windows, Mac Os, Mobile & Web.
It doesn't matter you offline or online, you can easily collect and store data. Evernote is a very strong alternative of Microsoft Office. At your Pc, mobile, windows or mac operating system any environment you'll be able to capture necessary data and Store it for next reference. Also can search text on image for its built in OCR (optical correcter recognition) system.
GMDesk
Website: www.robertnyman.com/gmdesk
Can be use at windows

You may know that, World famous search engine Google launched a lot of application that can be use online only. But GMDesk is one of applications of google that you've to install at your PC. also you'll need one software named Adobe Air(made by adobe cross platform run time environment) to use GMDesk. With GMDesk you will be able to use Gmail, Google reader, google desk programme etc.