Is there something similar to Office for Windows but free? I am student living on a budget, Office is not an option at the moment.
There are a number of web-based Office services that are also free and offer some of the functionality of Microsoft Office, including:
While these tend to lack the more advanced features of client-side Office suites, they do have excellent collaboration features.
Search for your school through the MSDN Academic Alliance. Even if it's not free, it will be significantly cheaper (to the tune of $30 or less).
You didn't specify if you need MS-Office interoperability.
For spreadsheets, there's also Gnumeric although they seem to be a bit unsure as to the stability of the windows build.
I use OpenOffice personally, which does a pretty good job overall, including easy production of PDFs, and MS-Office interoperability as far as Word and Excel goes.
And of course, there's Google Docs that others have mentioned.
Libre Office is another new kid on the block, created by former OpenOffice.org developers who left following the Oracle buyout of Sun. It's fairly new but releases seem to be coming thick and fast!
I know it's not free, but you can get Office 2007 Ultimate for $60 if you are a student. All you need is a .edu email address. Just go to www.ultimatesteal.com.
Thanks to Gnoupi, here is the French version.
If your school does not offer a cheap education version of office, Microsoft does make a $70 home and student edition if you need maximum compatibility.
EDIT: Newegg mentions a 3 user licence. So maybe you can get 3 people to go in on one.
You might check out Lotus Symphony.
Another alternative not yet mentioned is LaTeX. It is not a wysiwyg editor like Word or Libreoffice, but it is specifically geared for publication quality typesetting, and especially useful for academic work. It has specific abilities to typeset math, and also has tools to work with a bibliographic database and automatically format your references and footnotes.
A good starting point for learning LaTeX is the wikibook.
See also the stackoverflow discussion is LaTeX worth learning today?
You may also want to try the Google office products: Google Docs, Google Spreadsheets and Google Presentation. Over the last year they have added a lot of features, such that now they are pretty close to what you'd find in a offie suite, minus the fancy features you'd never use. They also export quite nicely to Microsoft Office and other formats when you need to and you don't have to worry about loosing your work when your computer crashes or the program/browser crashes (they save automatically, almost too automatic).
Another option/new commer is Office Live--Microsoft's answer to Google Docs, etc. It has some nice features that Google Docs doesn't have, but is also free...so you can use both :)
Here is a comparison between the 2: http://www.pcworld.com/article/168309/microsoft_office_vsgoogle_docs_a_web_apps_showdown.html There are ofcourse many other comparisons out there.
Edit Another possibility is OpenGoo. It's an open source solution that you can install on your own server and manage yourself.
ThinkFree is actually a well executed Java clone of Office, and its free.
There was another one that did PowerPoint only, and did it really well, but I can't remember the name of it now
SoftMaker Office 2010 for example. Perfect alternative, cheap, fast, lightweight.