Avira Antivirus Personal - Free Edition
Ccleaner, Extremely handy for clearing up garbage from the Computer
Defraggler, a convenient Maintenance Tool
Malwarebytes, very nice Anti-Malware (Virus, Spyware, Trojans, etc.)
Stardock Fences - Let's you organize your Desktop just like KDE does
aChat - Local network messenger for within your office for ex
