Clamwin is the best open source antivirus available for Windows 98/ME/2000/XP/2003 and vista. Clamwin comes with an easy installer and an open source code. You may download the full version and use it free of cost!!
Alien arena is one of those fast paced deathmatches with rich, colourfull, arcadelike atmospheres. The game includes some best features of Quake III and Unreal tournament and wraps them with a retro-alien theme. The game has tons of original ideas making it quite unique.
Moreover its an open source product guys!! Download the full version now..
Ubuntu is a sommunity developed operating system that is perfect for laptops , desktops and servers.. This is designed with security on mind. It is one of the best Linux distributions and is a open source OS just like other Linux versions.
Ccleaner formerly Crap cleaner is a system optimization and privacy tool. It removes unused and temporary files from the system allowing the windows to run faster , more efficiently giving you more harddisk space.
Metasploit is a opensource software useful to people who perform penetration testing , IDS signature development and exploit research. The software provides information on the exploit techniques i.e it identifies the bugs present in your current application...!