VirtualBox - Best free desktop virtualization

VirtualBox is a very good desktop virtualization software from Sun Microsystems that is available for free. VirtualBox runs on Windows, Linux, Macintosh and OpenSolaris hosts and supports a large number of guest operating systems.

Truecrypt - Free on-the-fly file and disk encryption software - UPDATE: Truecrypt is no longer recommended - Migrate to Veracrypt

Truecrypt is for the paranoid user who needs to have his/her files or partitions encrypted on the fly [no user intervention], once you have configured the software. It is an open source software available for free. Check out all the features here. The software runs on Windows, Mac, and Linux.

Truecrypt is no longer supported. Users are advised to migrate to https://www.veracrypt.fr/

OpenOffice - An excellent free alternative to Microsoft Office

Openoffice is available for free for use an alternative to Microsoft Office. Download it from http://download.openoffice.org/index.html. Many institutions across the world are using this software. The software can install and run on Windows, Mac, and Linux. If you need to send any of the documents produced from Openoffice to anyone who needs it in a Microsoft format, you can do so. You can even open Microsoft formats with Openoffice [You will need to wait for OpenOffice 3 for Microsoft Office 2007 documents] . The upcoming OpenOffice 3.0 release has many features that would it make it a serious contender to Office 2007.

Peazip - Free file and archive manager utility

PeaZip is a free, open source file and archive manager.

It allows you to open archives of the following types:

• ACE, ARJ, CAB, CHM, COMPOUND (MSI, DOC, XLS, PPT), CPIO, ISO, Java (JAR, EAR, WAR), Linux (DEB, PET/PUP, RPM, SLP), LHA/LZH, LZMA, Mac (DMG/HFS), NSIS, Open Office files, PAK/PK3/PK4, RAR, SMZIP, U3P, UDF, WIM, XAR, XPI, Z/TZ.
  

It allows you to create archives of the following types:

• 7Z, ARC, BZ2, GZ, PAQ/LPAQ, PEA, QUAD/BALZ, TAR, UPX, ZIP

PeaZip allows to save archive's layouts; apply powerful multiple search filters to archive's content; handle multiple archives at once; export job definition as command line; bookmark archives and folders etc.
Other features: AES256 encryption, robust file copy, split/join files (file span), secure file deletion, compare, checksum and hash files, system benchmark, generate random passwords and keyfiles.

PeaZip is cross platform, available as portable and installable software for 32 and 64 bit Windows (9x, 2000, XP, Vista) and Linux.

Miro - Free Media Player and so much more

Miro is a media player that can play any format [MPEG, Quicktime, AVI, H.264, Divx, Windows Media, Flash Video, and more]. It is just not a mediaplayer. Check out the features at http://www.getmiro.com/features/. It works on Windows, MAC, and Linux. Best of all, it's free.