I designed this list to aid my friends in their various PC and Mac labors.  Unfortunately, most of my experience is Linux, BSD, and Windows.  My BSD experience translates to Mac because the underbelly of the Mac is BSD/Unix.  The command line of a Mac will expose a plethora of tools taken from the Unix world.  Here I offer a laundry list of tools I like to use, mostly on Windows but on Mac, Linux, and FreeBSD where available.

My list of essential Windows tools

• 7-Zip handles practically any zip version you could imagine. It will decompress tar, gz, rar, zip, bz2, rpm, arj, cab, cpio, 001, and deb files. It also allows for plugins to add further file type support.
• Adobe Acrobat Reader or Foxit PDF Reader are essentials due to the ubiquitous nature of PDF documents. Foxit is lighter, much faster, and a smaller install. It's preferable on a system with limited resources, like a laptop. Adobe's tools can be resource hounds.
• Avast is completely free, lightweight, and effective. No antivirus is impervious to bad (user) behavior. However, this tool allows you to add an element of protection while not requiring you to open up Active X controls or slow your PC down with a bunch of bloatware.  I especially like the script blocking tool, which will stop a multitude of website based assaults on your Windows PC.
• Audiograbber, because we all listen to mp3s and it makes it very easy to rip them from your CDs.
• Burnatonce allows you to burn ISOs, and has a very simple interface to help you create CD images. It's not a robust point and click interface like so many commercial CD burning tools. But, seldom fails to perform. It's a nice, tiny CD burning tool.
• Filezilla, from the people that brought you Mozilla (and Firefox) gives you point and click command of FTP and FTP over SSL and SSH2.
• Firefox is the smaller, Mozilla family browser that allows tabbed browsing and various plugins and extentions that makes browsing much more pleasant and useful.
• Irfanview is a very utilitarian image editing tool that allows you to quickly create a batch of thumbnails, modify images, crop, modify size, change color scheme, file type, etc.
• Notepad ++ is an extremely lightweight and useful text editor. It offers tabbed file edits and color coding for code tags.
• Open Expert can be useful for Windows power users because it "enables you to specify any number of suitable applications for each file type."
• Open Office handles most any Microsoft Office document with more efficient use of resources and most importantly, FREE! It includes a spreadsheet, presentation, document (writer), html WYSIWYG, and other document management essentials.
• Putty is a free Telnet, SSH1, and SSH2 client.
• Tight VNC makes sharing desktops (relatively securely) between Linux, Unix, or Windows PC and laptops painless. It takes all of five minutes to set up a server and client. The windows ap is extremely simple and very light on resources.
• Trillian is a simple, though somewhat heavy, instant messenger that allows you to combine all your IM worlds in one tool: MSN, Yahoo!, AOL, Google, and Jabber (used by Google's IM network). It doesn't have painful popups, which is my primary reason for using it over any proprietary IM client.
• True Crypt Open gives you the ability to hide data and encrypt it. If you are carrying any type of work related data with you, it's essential you protect it. Encryption isn't bullet proof, but it adds a layer of security.
• VLC video player or BSplayer that plays MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, and a ton of other codecs.
• Winmerge allows you to do a "diff" or compare to similar files to see quickly what the differences are and select your preferred version of each difference, saving your munged version to a new (or old) file. There's much better programs out there, but this one is extremely simple, mostly functional, and free.
• XviD allows you to view Divx. If you're going to watch these video files, it's important not to install some adware, etc.
• Songbird is an Open Source music player.  The nice thing is that it supports open standard codecs and will likely grow in popularity and functionality due to its Mozilla roots.  From the website: "Songbird supports MP3, FLAC, and Vorbis on all platforms; WMA and WMA DRM on Windows; and AAC and Fairplay on Windows and Mac."

My productivity tools (some cost/overlap with the essential free tools)

• Adobe CS3 Web. Since I've had some problems that could indicate data integrity issues, I'm going to re-download this from my Adobe account. I may just check the md5 hash before I download it. The files are in the archives dir also. I bought this as an upgrade. So, I've got the older version's key and this version's key in my serials file. I've committed my account credentials to memory.
• Avast, which I'll download from their website for the latest version. I've got a commercial license, so I check my serials file. Got it!
• Apple iTunes, much to my embarrassment. It's just so easy. And, it'll move smoothly to my Mac when I buy it. The big download includes the latest QuickTime player also. It's important to unregister this PC before moving on. My music is in my archive. I've committed the account information to memory.
• Audacity because I often just want to record some audio and mix it down fast and free. My projects are in my archives.
• BitTorrent because Debian Linux and websites like that belonging to forward thinking music groups distribute cool stuff that way. Technology isn't just for piracy. I'll download the latest version.
• Camtasia Studios to record screen casting in Windows easily. The key is in my serials file. I can either download it from the website archives or use my archived install file.
• Digsby is the ultimate IM for Windows. These guys update so often there's no point avoiding the download - I'll just download the latest version. I've memorized my account.
• Foxit Reader - I love this software because it's faster and lighter than Acrobat Reader. But, I've got CS3 with Acrobat Pro, and it's tolerable. So, I'm dumping this software. No backup; no serials. Unfortunately, it's not as useful for a developer who uses Adobe tools. There's just no point.
• Free Commander because you just SHOULD have a backup file manager. I'll download it, and it's freeware.
• because I've got both 2100 and 2600 laser jet printers. Only, I need the CD since for some reason the dowloaded drivers won't load the network drivers on the 2600. I'm actually missing this CD. An employee had this in my basement about six months ago, so it's around. I'll put it on my list.
• IrFanview for down and dirty fast image editing via this freeware which I'll download to get the latest version. I've not upgraded in a while. Beware of the Google toolbar (watch install closely and don't miss opportunity to uncheck) - but glad it's free. Most free and even much commercial software install stuff you don't want. Watch all fresh installations carefully.
• Duplicate File Detective is commercial, but only about $40. I've used it before, and will likely use it again. But, it's awfully rudimentary in some respects. Maybe I'd be better off managing my drives with simple BSD commands - but I'll keep this URL handy to download it to search through my archives to make sure I've got few duplicates. I tried out Apple's automatic music management once and it made a mess of my collection. This tool helped me clean it up quite a bit, but it's something you'll need to closely watch. It doesn't remove emptied directories (or at least not with the configs I used).
• Macromedia's Flash Paper is now owned by Adobe. I may want to buy this to do some work for a few clients. I don't quite get flash paper, but apparently folks dig it. I think flash alone, maybe some actionscript work will suffice.
• Java because the JRE necessary for all kinds of stuff. I'll just download the free latest download on the Java website.
• Mozilla Backup because I've been using a Windows email client lately instead of SSH into a mail server and MUTT, which is much more comfortable to me. I mean, I've read and written my email in VI for 8 years now. To be blunt, I don't like using Mozilla, but I've got a lot of email and contacts, so I'm backing it up. I think I'm going to write something web-based to do this for me so I can use something like IMAP, web-based tools, and Mutt.
• Mozilla Add-ons for Firefox, cause I've got cool useful tools. I'll just download the latest and my bookmarks service password is committed to memory.
  • Web Developer
  • Foxmarks, though I've written up my own standard for a bookmarking tool in late 2000, and will launch it soon. Make sure I sync before moving on. My password is committed to memory.
  • Selenium IDE, to test web applications
  • Lola, for web design.
  • Skype, so I can call call and communicate via my Skype account easily.
• Nero to burn CDs and do minor DVD authoring. My key is in the serials file. I've got the lastest version for which I'm licensed. If I can download another copy, I'll prefer that one for the install.
• Notepad++ is an essential Windows Notepad replacement tool, free to download which I will do to get the latest clean version.
• Open Office.org because I prefer the simple predictable behavior and its price: free. I can install it on as many PCs as I like, and it creates and reads proprietary files like Microsoft Office (version XP and earlier).
• Pixie helps with fast web design on the fly. Mouse over any color in any application and copy its HTML color.
• Pidgin IM for a backup IM client for all major networks. I'll use the copy in archive or download the latest if I decide to install later.
• Safari because I develop websites and 14% of all computers sold last quarter were Macs. I'll download it from Apple.
• Registry Mechanic is the lazy man's registry cleaning tool. I bought it, and the key is sitting in my email inbox, and is not in my serials file (must not have thought it important). I've collected it and placed it in my serials file. Like many tools, it requires a matching registration name and key. Both were in an archived email (luckily I recognize my name).
• Sigmatel drivers because my little brother gave me a portable phone I use on my Skype account. I'll download it.
• Skype for my phone services and teleconferencing service. I've committed the credentials to memory.
• Delta Copy is freeware and I'll download the latest version. It's an rsync tool to synchronize an incremental backup of archive files from my Windows box to my local or remote unix server.
• Winamp because I still use it occasionally to listen to flac files. It's freeware, and I'll download it when I want to use it.
• WinSCP to move files around in SSH.

Mac users' essential tools

• Smultron Mac text editor, very versitile and gives you a clean and powerful interface to edit plain ole text.
• Until I put up more mac links, you may want to check out Pure Mac's lists