Free Software Resources

CCleaner - Clears unwanted and temp files from Windows, reclaiming system speed

Auslogics Disk Defrag 3 - A powerful windows defrag application

GPG4Win - File Encryption for windows

Malwarebytes - Anti-Malware Software

ThreatFire - Powerful behavior based supplement to anti-virus

Spybot Search & Destroy - Anti-Spyware / Spyware Removal Software

Anti-Virus

Avast Anti-Virus - A powerful anti-virus package that is free for non-commercial use

AVG Anti-virus - Another free anti-virus program

ClamWin - ClamWin Free Antivirus is used by more than 600,000 users worldwide on a daily basis. It comes with an easy installer and open source code.

Peer To Peer

Vuze - HD Video & Torrent Software

uTorrent - Small but powerful torrent software

Maps

Google Earth - Explore the world in 3D from anywhere.

Software Development

Eclipse - Powerful cross platform Java IDE

Netbeans - Create professional desktop, enterprise, web, and mobile applications with the Java platform, as well as C/C++, PHP, JavaScript, Groovy, and Ruby.

CodeBlocks - C++ IDE built to meet the most demanding needs of its users. It is designed to be very extensible and fully configurable.

IDLE - The Python IDE built with the tkinter GUI toolkit.

Linux Operating Systems (Advanced Users Only)

Ubuntu - Super-fast and great-looking, Ubuntu is a secure, intuitive operating system that powers desktops, servers, netbooks and laptops. Ubuntu is, and always will be, absolutely free.

Fedora - Fedora is a fast, stable, and powerful operating system for everyday use built by a worldwide community of friends. It's completely free to use, study, and share.

BackTrack Linux - A linux distro for penetration testers & security experts. "BackTrack is a Linux-based penetration testing arsenal that aids security professionals in the ability to perform assessments in a purely native environment dedicated to hacking. Regardless if you’re making BackTrack your primary operating system, booting from a LiveDVD, or using your favorite thumbdrive, BackTrack has been customized down to every package, kernel configuration, script and patch solely for the purpose of the penetration tester."

File Compression

7Zip - Zip, 7z, and other compression formats

Virtualization

Virtual Box - VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL). See "About VirtualBox" for an introduction.

Presently, VirtualBox runs on Windows, Linux, Macintosh and OpenSolaris hosts and supports a large number of guest operating systems including but not limited to Windows (NT 4.0, 2000, XP, Server 2003, Vista, Windows 7), DOS/Windows 3.x, Linux (2.4 and 2.6), Solaris and OpenSolaris, and OpenBSD.

Qemu - QEMU is a generic and open source machine emulator and virtualizer.

When used as a machine emulator, QEMU can run OSes and programs made for one machine (e.g. an ARM board) on a different machine (e.g. your own PC). By using dynamic translation, it achieves very good performance.

When used as a virtualizer, QEMU achieves near native performances by executing the guest code directly on the host CPU. QEMU supports virtualization when executing under the Xen hypervisor or using the KVM kernel module in Linux. When using KVM, QEMU can virtualize x86, server and embedded PowerPC, and S390 guests.

Misc

Synergy - lets you easily share a single mouse and keyboard between multiple computers with different operating systems, without special hardware.

Portable Apps - Many of the popular apps above, capable of being run from a flash drive

Linux Portable Apps - Popular portable linux applications

FileZilla - Great FTP client, standard & secure ftp

UltraVNC - Manage another computer remotely

Google Calender - Google online calender

TeamViewer - Manage another computer remotely (free for private use only)

DropBox - Free & Paid Online Backup / Cloud File Storage

Mozy - Free & Paid Automatic File Backup / Cloud Storage

Grooveshark - Listen to Free Music Online - Internet Radio