Open Office- http://www.openoffice.org
Open Office is an alternative to the popular Microsoft Office suite, and includes tools such as a word processor, spreadsheet, presentation tool and database. Open Office interacts well with files generated from Microsoft programs – such as .doc, .xls, .ppt files, and can even open newer file formats (.docx, .xlsx) easily! Open Office is available for Linux, Windows and Macintosh platforms.
FreeMind – http://freemind.sourceforge.net
FreeMind is a free mind-mapping application that allows you to graphically brainstorm concepts, lists and ideas. It is an excellent tool for studying and planning. FreeMind is available for Linux, Windows and Macintosh platforms, and is based on Java.
Zotero – http://www.zotero.org/
Zotero is a free add-on for the Firefox web browser which allows you to store, collate and export academic references in a variety of formats. You can also share your citations with other researchers. Plugins for Open Office and Microsoft word are also available.