List of Free or Open Source Security softwares that can compete with their shareware alternatives

Here is a list of free or open source softwares that can compete with most of their shareware alternatives..And almost in all categories we have got pretty good list of capable softwares..So,I thought why not prepare a nice list of good open source and free softwares that will be useful to lot of pc users..I know it is quite a difficult task to prepare such list and it can never be considered complete..So please help me in making this list as comprehensive as possible..

Antivirus /Internet Security Suite
* AVG Anti-Virus Free 9.0.851 Build 3009

Supported platforms: 2000/ XP/ XP Pro x64 Edition/ Vista/ Vista x64 Edition/ Windows 7/ Windows 7 x64 Edition
     Homepage - http://free.avg.com
      Size: 89.5 MB

Download Freeware

*  COMODO Internet Security 5.0.158836.1079/ 4.1.150349.920

    Operating systems: Windows 7 / Vista / XP SP2
Homepage - http://www.comodo.com
Size: 47.4 MB


Download COMODO Internet Security 5 for Windows 32bit
Download COMODO Internet Security 5 for Windows 64bit

Download COMODO Internet Security 4 for Windows 32bit
Download COMODO Internet Security 4 for Windows 64bit

Download COMODO Internet Security 3.14.130099.587 for Windows 32bit
Download COMODO Internet Security 3.14.130099.587 for Windows 64bit

* Microsoft Security Essentials 2.0.375.0 Beta/ 1.0.1963.0

Well it is free for only genuine Windows users..But it has got some nice reviews,so there is no harm in trying it out.. ALL-IN-ONE INTERNET SECURITY. Comprehensive Internet protection featuring antivirus, firewall, antispam, web safety and proactive defense tools.
Homepage - http://www.microsoft.com/security_essentials/
Size: 11.3 MB
Download Microsoft Security Essentials 2.0.375.0 Beta

Microsoft Security Essentials 1.0.1963.0 All Downloads
Download for Windows XP 32-bit
Download for Windows Vista/WIN7 32-bit
Download for Windows Vista/WIN7 64-bit

Download Latest Definitions 32-bit
Download Latest Definitions 64-bit

* avast! Antivirus 5.0.594 - Final

Its latest version is pretty solid and is very highly rated..
Works on Microsoft Windows 2000, Microsoft Windows XP/Vista/7 (32/64 bit).
Homepage - http://www.avast.com
Size: 45.3 MB
Download avast! 4.8.1368 Home Edition - Free
Download version in your language

* Avira AntiVir Personal 10.0.0.567 - FREE Antivirus (Updated)

Operating systems:
- Microsoft Windows 2000, SP 4
- Microsoft Windows XP Home or Professional, SP2
- Microsoft Windows Vista (32 or 64 Bit)
- Microsoft Windows 7 (32 or 64 Bit)
Homepage - http://www.free-av.com
Size: 42.0 MB
Download
Mirror

Malware Removal Tools
* Malwarebytes' Anti-Malware 1.46

Even though the Full version is not free,the only different between the full and free version is that there is no online protection.But it is very effective tool to clear malware and spyware infections
Homepage - http://www.malwarebytes.org
Size: 5.86 MB
Download

* Dr.Web CureIt 6.00.2.05140 [2010-08-15]

This utility can quickly clean an infected system, but it is not a permanent tool to cure your computer in case of infection.

Homepage - http://www.freedrweb.com
Size: 46.1 MB
Download

* UnHackMe 5.95 Build 348

This is a great utility to have for clearing virus and other rootkit infections.But it is advised only for advanced computer users.
Homepage - http://www.greatis.com/unhackme/
Size: 9.43 MB
Download UnHackMe Stable

Anti-Spyware Tools 
* Spybot - Search & Destroy  1.6.2.46 - Final

The best free Antispware out there and infact a must have software on any computer as far as security is concerned.
Homepage - http://spybot.info
Size: 15.6 MB
Freeware
Download SpyBot - Search & Destroy 1.6.2 Final
Mirror
Download Update

*SUPERAntiSpyware 4.41.1000

Homepage - http://www.superantispyware.com
Size: 8.73 MB
Download SUPERAntiSpyware Free Edition 4.41.1000 Final
Download SUPERAntiSpyware Portable Scanner

Firewalls 
* Comodo Firewall 4.1.150349.920

One of the best and most highly rated firewall

Homepage - http://personalfirewall.comodo.com
License: Freeware
Size: 55.8 MB
Download x86
Download x64

* Online Armor 4.0.0.45

Online Armor runs on Windows XP, Vista, Windows 7 32 bit only - Win 64 is in Beta.
Size: 11.6 MB
Download Online Armor FREE

* ZoneAlarm Free 9.3.014.000

Homepage - http://www.zonealarm.com
Size: 44.5 MB
Download ZoneAlarm Free


*  PC Tools Firewall Plus 6.0.0.88

Platforms: Designed for Windows 7 (32/64bit), Vista (32/64bit) and XP (32bit)
Homepage - http://www.pctools.com/firewall/
Size: 10.2 MB
Download Final