This review is done by Ashwin who is our Mod at Avinashtech Forum and one of the top contributors there even having post counts greater than mine. He also blogs at Ashwingeek.

Review of Avast! Free Antivirus 5.0.594
(This review does not include virus tests, just the features)

My PC’s config:
Win XP Home SP 3(fully patched).
Intel Pentium Dual Core 2.40 GHz
2 GB RAM and 350gb SATA HDD

I am currently using Avast! Free Antivirus 5.0.594and Comodo FW 4.1.150349.920 on my PC without any conflicts or slowdowns in boot-time, regular performance or network speed. Avast! Free Antivirus comes with a ton of features that are not even available in commercial anti-virus products.

I am quoting the features of Avast from avast! Free Antivirus – Download Software for Virus Protection. Visit the above link if you want to know more details about each feature.

Core and Detection
Antivirus and anti-spyware engine
Real time anti-rootkit protection
avast! Community IQ
Code emulator
Heuristics engine
Potentially unwanted programs detection

Scanning
Boot-time scanner
Wake-up for scan
Scheduled scanning
avast! Intelligent Scanner

Shields

Behavior Shield
Behavioral Honeypots
File System Shield
Mail Shield
Web Shield
P2P Shield
IM Shield
Network Shield

Misc
Smart virus definition updates
Fast application of updates
Silent/Gaming Mode
Multi-threaded scanning optimization
Green computing
avast! iTrack
Graphical user interface
Automatic processing

What more could you want from an Antivirus, and trust me all this comes for FREE. Visit this link to download Avast! Free Antivirus (English version) Download Avast! Free Antivirus 5.0.594. Avast supports many languages, if you want other languages than English, visit this link avast! Free Antivirus – Download Software for Virus Protection

You can also install additinal languages from Avast interface. Go to Settings>Languages and check the languages you want to install

System requirements:

* Processor Pentium 3, 128 MB RAM, 100 MB of free hard disk space
* Microsoft Windows 2000, Microsoft Windows XP/Vista/7 (32/64 bit)

Screenshots of Avast that I took from my PC:

File system shield:
This shield scans files that are currently in use (active files)

Mail Shield:
I use ThunderBird and Avast gave me a warning to disable SSL/TLS security in Thunderbird. After I disabled this in ThunderBird, Avast was able to scan all my mails for infections.

Whenever a new mail is received, Avast Mail shield will automatically check it for infections


Webshield:

This shield protects your PC from infections/scripts from the webpages you visit. (Does not slow your browsing speed)

Network Shield:
This shield protects your PC from potentially dangerous websites. It will automatically block your browser from loading such websites. An automated voice message alert will be played after a malicious url/threat has been blocked.

I tried accessing a proxy website, Avast blocked it automatically and prevented FireFox from loading the site.

Comparison of Avast free and commercial versions, surely the free version is outstanding and provides perfectly good security even for a new user.

Besides these shields, there is
1. IM Shield: protects you from threats distributed via Instant Messengers
2. P2P Shield: Protects your PC while using p2p file sharing programs like Utorrent, bittorrent, etc.

Updates:
Updates are regularly available, automatically downloaded and fast. An automated voice message alert will be played after an update is performed.

Scanning types:
Quick scan: Scans the memory and system volume

Full system scan: Scans the entire Harddisk

Removable media scan: Scans removable media like CD/DVD, USB flash drives (pen drive or memory stick), memory cards.

Custom folder scan
: Scans any folder of your choice. Besides this, there is also a Context Menu item which allows you to scan any folder via windows explorer.

Boot time scan
: A very useful feature, it scans the PC before Windows is loaded, helps remove stubborn malware.

Avast has a couple of special scans available if you enable them in Settings>Basic Settings>Special scans

Here is a screenshot showing Avast with the scans available by default

Now to open Avast’s Settings

Enable the Special scans by ticking the checkbox as shown in the screenshot below

Now the New scans are available as shown below

Important Tip to make to speed up Avast scans :
To make the Full System Scan even faster, configure it to actually take advantage of the persistent cache. To do this, open the Full System Scan details, click the Settings button and check the box “Speed up scanning by using the persistent cache” on the Performance page.

Source: avast! blog » How to make the Full System Scan 6x faster in 10 days

To go to full scan details:

Now click on settings for Full Scan:

To enable Persistent Cache,

License registration:
Avast! Free Antivirus requires free registration after 30 days of usage.
Avast can be registered in two ways, 1. From their website and 2. through the Avast interface

Registration through the interface is easier and faster.
You need to provide your name, email id, choose your age group and answer an optional question to register for a free 1 year license.

Summary:
I find Avast! Free Antivirus to be very light on resources, scans are blazing fast and reliable.
Besides Avast and Comodo, I also use SuperAntispyware, Malwarebytes antimalware, Winpatrol and Spybot to keep my PC free from infections. (All four have free versions available)

I recommend you to try Avast! Free Antivirus before buying any commercial AV.

PS: This review was originally posted at Avinashtech Forum.