Chrome has overtaken Firefox to become the best all-round web browser, although in the last year or so Firefox has made marked improvements. Chrome’s advantages over Firefox are speed, stability, and aesthetics. But there are lots of alternatives, notably Webkit (which is both free and open source) as well as Opera, Safari and Internet Explorer (which are free but not open source).
LibreOffice (which is a fork of OpenOffice) provides you with a free Office suite that’s highly compatible with Microsoft’s products, and actually has a few extra tricks up its sleeve (such as a dedicated drawing program).
DropBox (not open source) is a small, free, easy-to-use program that gives you a folder that lets you sync files between computers without bothering with USB sticks, keeps old versions of files around for 30 days in case you accidentally delete something, and, perhaps best of all, makes it easy to share files and folders with other people. Alternatively, Amazon has just introduced a similar service called Cloud Drive (web service) that offers more free space (and cheaper additional space) but none of the convenience.
For those cases when you need a real text editor (e.g. for programming or editing web pages) you’ll want Notepad++ (on Windows) or Textwrangler (on the Mac, not open source) or Komodo Edit (not open source) on either. If you’re happy using the command line you have plenty of options (and you don’t need my help!).
Darktable is an open source replacement for (and blatant imitation of) Adobe Lightroom, which means it’s also a replacement for Aperture, iPhoto, or the late, lamented Picasa. It’s under active development, and already quite powerful. If you’re familiar with any high-end photography or image manipulation program you’ll pick it up in no time.
Handbrake is great for ripping DVDs so you can play them from your hard disk (e.g. on a media center computer) or mobile device (iPod, iPhone, Zune, PSP, etc.). It won’t work on some DVDs (but neither will commercial packages).
If you need a free alternative to Photoshop you should look at The GIMP, although Mac users may find the X11 user interface a bit hard to take. If you need an alternative to Illustrator there’s also Inkscape (with the same caveat for Mac users).
And finally, Audacity is a must-have application for anyone who needs to edit or sequence audio files.
The programs discussed thus far only scratch the surface of what’s available. All software discussed on this site is organized into categories (what does it do? what does it run on?) and the commercial packages they can replace (OK I need something like Excel…). I hope you find the information on this site useful, informative, and easy-to-find.
All of these programs and services are available for free, but not all are open source. I explain why non-open-source software is mentioned on this site elsewhere.