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.

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

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?

Download Avast! Virus Home Edition | Price: Free

Communicate, Copy, and Protect

If you need to capture or annotate screens for any reason--and who doesn't?--you need this program. It's simply the best screen-capture app you'll find anywhere. With SnagIt you can capture entire screens, portions of screens, active windows, menus, or scrolling screens. Or use its built-in timer to capture screens after a given amount of time. Grab screens with the cursor visible, or eliminate the cursor. And save your capture in any major graphics format. On top of all that, you can print the captured image, send it via e-mail, send it via an instant messenger program, and more.

Want to add special effects to your capture? SnagIt can do that as well, automatically adding drop shadows, watermarks, and many other effects as you direct. The program also has a very good editor for annotating screen shots, and an image browser for looking through graphics on your PC.

Download SnagIt | Price: Shareware ($40)

Want to rid your PC of unnecessary programs that run on startup, and help keep it free of spyware and other forms of malware? How about doing that for free--and getting other nice freebies as well, such as a cookie remover? WinPatrol 2007 delivers all that and more, conveniently and intuitively.

Set up WinPatrol, and thereafter whenever a program tries to add itself to the set of apps that start up automatically when Windows boots, you get an alert that invites you to block interloper. Click WinPatrol's Startup Programs tab, and you'll see a detailed list of every program that your PC automatically launches at system startup--including the app's manufacturer, the date the app was added to the startup set, and its file name. A clever feature called Delayed Start lets you tell certain programs to delay launching for up to an hour after Windows boots, so Windows can start up quickly and the program can still load later on. You also get a list of all the Internet Explorer add-ins currently running, along withthe ability to remove any you don't want to keep.

Download WinPatrol 2007 | Price: Free

If you enjoy social networking sites and believe that the Web is as much about connecting to other people as about connecting to Web sites, this browser for you. It's particularly useful if you participate in multiple social networks, such as Twitter and Facebook. In a left-hand pane, it lists friends from all of your social networks, so you can quickly see any changed information about them--an updated profile, say. You may also share media and Web content with them.

In addition, it displays photo and multimedia content from sites like YouTube and Flickr in a kind of scrollable filmstrip. Grab any photo or multimedia media thumbnail with your mouse, drag it to a friend's profile on the left-hand pane, and they'll be able to see it.

Increasingly, businesses are using social networking sites; if you find that work is drawing you to use such sites--even if you have no interest in them as leisure-time destinations--you may want to make Flock your browser of choice. ( Editor-in-Chief Harry McCracken wrote an in-depth review of this browser in October 2007.)

Download Flock  | Price: Free

For years, without the assistance of third-party software,users of AOL Instant Messenger haven't been able to communicate with users of Yahoo Messenger or users of MSN Messenger (or whatever Microsoft calls it these days), and vice versa.

That's where this freebie comes in. From one clean, simple interface, you can communicate with anyone who uses AOL Instant Messenger, Yahoo Messenger, MSN Messenger, or ICQ. It's easy to add new buddies and accounts; you can organize contacts in any way you want; and small, colored buttons show you which instant messaging networks each of your contacts uses.

Trillian simplifies switching from your current instant messaging program because it imports all of your passwords, contacts, and buddy lists. Other pluses: You can check your e-mail on the various services; and Trillian supports video chat and audio chat.

Download Trillian Basic | Price: Free

Power Tools

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

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.

Download IrfanView | Price: Free

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

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.

Download CCleaner | Price: Free

More Must-Haves

This utility removes "craplets" and other junk that commonly come pre-installed on new PCs. But it's useful for cleaning up older PCs, too, because they fill up with junk of their own.

TAmong the space-wasting dross that this program removes are AOL's installation program, McAfee and Norton programs, and MusicMatch. Run it, tell it what to dispatch, and it quickly goes about its work.

Download PC De-Crapifier | Price: Free

If you live to download, this free program can solve just about every download problem you have. To accelerate downloads, the utility divides them into pieces and then downloads the pieces simultaneously from the fastest servers it can find. The program claims it can improve download speeds by up to 400 percent. Mmmmaybe. It certainly gets downloads onto your system faster, particularly when you're downloading multiple files.

The program automatically launches and begins work when you specify that you want to download a file while in your browser. You can add downloads to the program manually, too, if you like.

Download Accelerator Plus can complete broken downloads, lets you pause and resume downloads, and gives you tools for managing all of your downloads. A useful history manager shows you all of the files you've ever downloaded, including their size and date of download. Double-click any entry in the history list, and you'll launch the downloaded file.

Get Download Accelerator Plus | Price: Free

MediaMonkey does a great job of organizing your music files, playing them, ripping and burning CDs, converting files into different audio formats, creating playlists, synchronizing music between your PC and your iPod or other MP3 player, and more. And it's free.

Extras include the ability to automatically look up and add tags to your MP3s, and the ability to automatically find album art. MediaMonkey is perfect for people who have large music collections, because its organizing tools are so superb, but any music buff will find it useful.

Download MediaMonkey | Price: Free

Sometimes the best choice for transferring files is the old-fashioned FTP protocol--say, when you need to transfer files too large for your ISP to tolerate, or when you need to transfer multiple files. On such occasions, FileZilla is a wonderful tool to have.

Despite being easy to use, this free FTP client provides a multitude of features such as the ability to configure transfer speed limits, and to resume the transfer of files larger than 4 GB. It supports every FTP protocol you might need, including FTP, FTP over SSL/TLS (FTPS) and SSH File Transfer Protocol (SFTP). And the site manager is superb and simple.

Download FileZilla | Price: Free

If you'd like to customize your version of Windows Vista to make it look different or perform better, Vista Manager can help. This app allows you to change aspects of the operating system at a granular level, and it helps you optimize your system's performance by adjusting its its RAM, cache, and hard-disk settings. It also cleans your system, improves your security, customizes the way your network works, and lets you manage system startup and shutdown.

As an example of Vista Manager precision, it gives you control over ten different settings for the Taskbar alone, plus another six for the notification area on the Taskbar.

Download Vista Manager | Price: $40 (Shareware)