As a frequent downloads reviewer for PC World, I look at lots of downloadable software every year--more apps than I care to count. As a result, each week, I encounter and test-drive the great, the not-so-great, and the feeble.

Every once in a while, a piece of software so clearly outclasses its peers that it deserves special commendation. For this article, I've assembled my 15 favorite dowloads of 2007, selected from a wide range of categories--everything from antivirus and security tools to system tweakers, from media managers to system speedups.

Among them you'll probably find some old favorites, but also plenty of unfamiliar apps that you'll grow to love.

Process Explorer

Do you really know what's running right now on your PC? In all likelihood the answer is no. Dozens of processes or services may run in the background without your being aware of it. And though it can show you what's running, Windows' Task Manager is a poor tool for diggng deeper than that.

Process Explorer (a free download) provides exceptionally detailed information about every process and service, as well as identifying any applications associated with them. In Task Manager, you have no idea what each process and service do. But because Process Explorer often shows applications associated with each process and service, you'll be able to tell whether shutting them down is safe. The tool can also uncover clues indicating that a service or process may be spyware or malware.

Download  Process Explorer | Price: Free

Avast Anti-Virus Home Edition

These days, most antivirus programs come as part of an expensive, bloated, RAM-hungry suite that sucks up system resources, slows your system to a crawl, and requires you to pay for a new subscription every year. If you're tired of paying through the nose for antivirus protection, and want a slim, svelte anti-virus tool that does everything that high-price software does, get Avast Anti-Virus Home Edition. It has everything you need in an antivirus tool--notably live protection to ensure that you don't get infected in the first place. It also protects against instant messenger viruses, e-mail- and Web-mail-borne viruses, and viruses spread through peer-to-peer file sharing programs. It also scans your system for viruses, and eliminates any it finds.

Avast Anti-Virus Home Edition is free and extremely customizable: You can change the level of protection that any of its individual shields provides from normal to high, or create your own customized rules. So ask yourself, do you really need your current, high-priced suite?

Power Tools

Comodo Firewall Pro

The firewall built into Windows XP includes no outbound protection. And the Vista firewall, though it provides some outbound protection, is remarkably user-hostile. Just try to configure the outbound firewall--it's nearly impossible.

Enter Comodo Firewall Pro, a top-rated free firewall that's easy to use and configure. This tool automatically protects your inbound connections; and for outbound connections, it notifies you every time a program attempts to make a connection. You can then approve the connection, if you recognize the program, or else forbid it.

An overview screen shows all of your current Internet traffic and maintains a history of defense and threats. The firewall is network-friendly, too: If you're on a home network when you first run it, the program will automatically recognizes this fact and ask you whether you want all of the other PCs on the network to be trusted.

Download Comodo Firewall Pro | Price: Free

age,1-c,tools/description.html">IrfanView

IrfanView is the best graphics file viewer and all-around utility you can get. It's lightning fast, displaying graphics files faster than any other editor or viewer. It lets you view graphics files and play video and audio files in dozens of formats.

In addition, IrfanView lets you edit photos and images--flipping, rotating, and resizing them; increasing their color depth; converting them to grayscale, auto-adjusting the colors; and removing red eye. It does a fine job of converting graphics files from one format to another, and it can handle batch conversions of such files, too.

age,1-c,tools/description.html">Download IrfanView | Price: Free

Launchy

This small, free, open-source program enables you to launch programs and open documents without having to hunt, peck, and mouse around.

When you install the program, nothing seems to happen initially. But press Alt-Space, and you'll see a big black empty box in the middle of your screen. Start typing the name of the program or file that you want to launch, and Launchy will display a matching list. Select the program or file from the list, and the chosen item launches. You can use wild cards, command-line options, plug-ins, and skins to customize a launch.

Winner of the community choice award for best new project of 2007 at the open-source site Sourcegorge.net, Launchy is simple, fast, useful, and free.

Download Launchy | Price: Free

CCleaner

Your PC and its applications are filled with junk that slows down your PC, consumes precious disk space, and may be used to invade your privacy.

The author of the free CCleaner claims that the utility has been downloaded 100 million times.  No wonder: It gets rid of such Windows junk as temporary files, log files, and Recent Documents. It cleans out files from multiple browsers, including Internet Explorer, Firefox, and Opera. It even removes junk from third-party programs such as Google Toolbar, Microsoft Office, Nero, and Adobe Acrobat. And it has a Registry cleaner, for cleaning junk from the sensitive Windows Registry.