Some of the most useful utilities for diagnosing problems with your PC and making it more pleasant to use are completely free. Here are some of our favourites.
An unmatched collection of tools to monitor all types of system activity - files opened, registry keys accessed, system threads, TCP connections, etc. Filemon, Regmon, and Process Explorer are the most well known tools, but there are many, many more. Now all the main tools are available as a single download for easy installation.
These tools used to include source code, which was invaluable for learning advanced Windows programming techniques, such as dynamically loaded virtual device drivers. Sadly, since Microsoft bought out the original founders, this code is no longer available.
One of the best disk de-fragmenters - equally at home under Windows XP and Vista. Runs in the background, no reboot required, and with a nice graphical display to show progress. Can also run as a screen saver.
A collection of tools to identify and remove assorted malware and adware from your system, all packaged neatly into a single one-click solution. If your PC starts behaving oddly, running ComboFix is a good first step. Updated regularly.
Finally, a way to easily rearrange the order of buttons on the Windows taskbar - just drag & drop buttons to position them where you like. Not a complicated utility, but very handy!
Microsoft's PowerToys for Windows XP
included the very useful ImageResizer
utility, which allows easy resizing of JPEG images from Explorer's right-click context menu. However, it doesn't work under Vista -- VSO's Image Resizer does.
If you're working with audio, you'll want a copy of this. With many, many plug-ins available, it's a straightforward way to record, edit and transform audio files of all kinds.
A comprehensive packet sniffer, invaluable for investigating network problems. One of its strengths is an open architecture that allows plug-ins to be quickly developed for new network protocols.
A bootable CD that includes a vast array of hard drive and operating system diagnostic tools, all accessible without having to boot into the host OS. Invaluable for data recovery and post-mortem.
A bootable CD that launches a stripped-down Windows system from which you can run a large number of pre-installed tools & recovery utilities, all without modifying the host system's hard drive. An essential component of any PC technician's toolkit.
It may be a little long in the tooth, but EasyCleaner still provides a good collection of registry & directory cleaners wrapped in a nice GUI. Particularly useful when faced with a Windows PC that has been run for several years with no periodic file maintenance. All the more impressive, when you discover the author was only 15 years old when he wrote it.
A decent drive recovery program, now discontinued. Its deleted files browser is one of the quickest ways to recover a lost file on an NTFS psrtition. With modern drive sizes stretching to hundreds of gigabytes in size, its low-level drive scan is less useful now but still occasionally handy.
Since the development moved to a commercial organisation, it is now increasingly difficult to find the free (and slightly buggy) older version, but it's well worth the effort.