Before I'm off to the list, let me tell you that you don't need any "qualification" to like these softwares. The average computer user might not feel the need for any of these, but I highly recommend each one. I'm not including any security software here, because I expect even the average computer user to feel the need to have them. :P
1.
CCleaner
This nifty tool was actually named "Crap Cleaner", and does everything the name promises, and more.
2.
Defraggler
Way better than the default Windows defragment tool.
Defragment your hard drive a couple times a year to keep it running fast and well. However, as I recently learnt (Thanks, Karan Kantoor), do not defragment too often, because moving large chunks of data on your drive needs lots of setting and resetting, and is therefore not good for the drive's health.
3.
Google Chrome
No matter what browser you primarily use, (I hope you don't say Internet Explorer :P) you should have Google Chrome installed. It's very fast, and comes with a generous set of features despite the minimalist approach, the "Incognito" mode being one of my favourites.
4.
Evernote
This powerful note-taking app is a must-have for almost everyone. Sign up for an account, and download the desktop client. There's an online account where all your information gets synced, and there are iPhone and BlackBerry clients too. Write notes, make lists, take screenshots... and I'll tell you more as I discover. MS Office fans might like OneNote for its similar features, but I appreciate Evernote's generous free plan too much to not use it.
5.
Recuva
This one can be a true life-saver, especially for fans of the dangerously useful
Shift + Delete combination. Pronounced
recover, this software does one simple job, and does it well
—recover files from your hard drive once you've permanently deleted them but they have not yet been totally effaced.
6.
Q10
Here comes my favourite text editor of all time. This is the software I'm using to type right now. There's a plain black background, covering my entire screen, green
Matrix-style text on it, and a bar on the bottom that helps me track the time, number of words, pages, etc. There are lots of customizable features, and this tiny software is also portable, so you can even take it on a flash drive anywhere you want to.
7.
Caffeine
This microscopically light app is a wonderful way to keep your computer active and awake. All it does is simulate a
Shift keypress every 59 seconds, to make sure your computer does not sleep or activate the screensaver if you don't want it to. And for the curious, the
Shift key is almost harmless, and indicates to the computer that a user is around.
8.
JPEG Lossless Rotator
The name really does say enough. Lossless Rotator has a very simple purpose: it rotates digital pictures in a way that does very little damage to their quality, if at all. It's very user-friendly and integrates directly into the shell, so all you have to do is right-click a picture and select "Lossless Rotate Left/Right".
9.
Foxit Reader
This is not really a must-have, because most of us use Adobe Acrobat Reader for pdf files anyway. But in case you're looking at better speed and features, Foxit is a quick answer. For a quicker one, check out
Sumatra PDF, a light, portable and ultra-fast pdf reader.
Edit:
Nitro PDF Reader. Period.
10.
Universal Viewer
If there could be a Swiss Army knife equivalent of softwares, Universal Viewer would be a contender, if not the winner. Under one common roof, you can open tons of file formats that cover pictures, audio, video, and lots more.
Most of these come with decent alternatives, also free. These are just my favourites, and they do their job handsomely. Some of these are Windows-only, so feel free to recommend cross-platform/Mac/Linux alternatives, and also share your own favourite tools in the comments.