I've been slowly but steadily moving to open-source platforms over the last few months. There are many reasons why and I won't bore you with the details; suffice to say that most of the major open-source projects are at worst almost as good as their commercial counterparts, free, cool and, from a developer perspective, there's always the option of tinkering.

Here's a selection of some of the more prominent open source programs I use:

• Things I use every day:
  

• Mozilla Firefox - the quintessential open-source project, which is lately getting even more spotlight than Linux itself. It has all the features you can hope for, is much faster than Internet Explorer, far better in the usability department (tabbed browsing, better download manager etc.) and is even compatible with about 90% bidi (Hebrew) websites. I've been using this since Firebird 0.5 (thanks, Ilya!) and it kicks mundo ass.
• OpenOffice.org - the Microsoft Office replacement that's actually better than Office itself (well, at least Impress and Writer are). A localized version in Hebrew can be found here.
• SpamBayes - open source bayesian filter, with Outlook plug-in. Fast and robust.
  
• FileZilla - great FTP client and server (on par with CuteFTP and BulletProof). Windows-only, though.
• The Gimp - photo editor. Not perfect, but as close to Photoshop as it gets without paying mundo bucks, and it's actually pretty damned good.
  
• 7-Zip - excellent compression tool, with command line as well GUI options, a full library and support for most popular compression formats.
• VideoLan Player - impressive open-source player and codec library. Self-contained and works great.
• JetBrains Omea Reader Pro - excellent news aggregator with a huge number of features I don't generally use (among other things, it synchronizes with Outlook to let you access notes and contacts, it has a newsgroup reader, and more). It's fast, stable and simply good, and best of all - it's about to be released as open source software.
• Notepad++ - terrific editor with syntax highlighting. It simply works.
  
• ffdshow - a terrific DirectShow/VFW codec pack, including XViD, DiVX and MPEG-4 video decompression filters. Great quality and performance. Make sure to Google for the latest build.
  
  
• Development tools:
  
  
• Eclipse - an extremely impressive, full-featured IDE which gives Visual Studio a run for its money.
• The Regulator/Regulazy - Roy Osherove's as-yet irreplacable tools for developing regular expressions (particularly with .NET).
• WireShark (formerly Ethereal) - the de-facto packet capture and analysis utility. One of the best debugging tools known to man.
• Cygwin - Posix environment for Windows, with GNU tools and everything. I'm not much of a UNIX guy, but this has proved invaluable in more than one case.
• NUnit - the most popular unit testing framework for .NET. Make sure to check out TestDriven.net (unless you use ReSharper, in which case the built in runner should suffice).
• log4net - Logging framework for .NET. Absolute must-have.
  
  
• Good tools I sometimes use:
  
  
• Audacity - solid waveform editor
• VirtualDubMod - best-of-breed DirectShow-based processors. I use this to encode, transcode and edit AVI files.
• DOSBox - an open-source DOS virtual machine, emulating slower machines as well as several audio cards. Great for running old games, although not perfect.
  

My open source wishlist includes:

• A proper, open source Norton Commander clone. Currently the best software in this category is, in my opinion, Total Commander, which has two major deficiencies: it doesn't support unicode, and it's commercial. Midnight Commander is Linux-only, text only and just doesn't cut it.