Whether your important data lives in the cloud, on your laptop, or on a different operating system, you shouldn't have to use sub-par tools to get at it. These downloads work with every major operating system, along with some not-so-major (mobile) ones.
All of these applications run on all three major operating systems—Windows, Mac OS X, and Linux—and most can be loaded onto a thumb drive and run as a portable app on any Windows system. Some can also be accessed from the web, and a few have dedicated mobile apps for most phone platforms. We've distinguished which apps work where at the front of each item. If we've missed any platforms, please tell us so (politely!) in the comments.
Computers: Buddi is a financial management application developed with financial non-experts in mind. Sure, it can import your CSV file from a bank or financial firm, and it does all the standard financial calculations and projections. But the way it switches between money figures, and walks you through the importing and setting up of your accounts, makes it a real open-source find, and you can easily swap profiles between your laptop and desktop systems, if needed. Looking for something with a bit more mathematical oomph? Money management alternative GnuCash has you covered.
Computers, portable, cellphones: You use a multitude of applications and web sites that require passwords, license keys, and administrator codes. On one computer alone, that makes it worth having a central vault for all that stuff. If you use more than one computer, having a consistent KeePass database is really, really helpful. Encrypt your master password database with a file only you have access to, and/or a truly secure single password, and you can take that list just about anywhere—on Windows, Mac, Linux, iPhones, Android, BlackBerry, Palms, on a USB drive, or pretty much anywhere. Open-source coders love to write KeePass apps, so there's a very good chance you'll always have this clever password management system at your side. For help getting started with KeePass, check out Gina's guide to securely tracking passwords. (It also works great in conjunction with Dropbox.
Computers: TrueCrypt is a multi-platform security tool for encrypting and protecting files, folders, or entire drives. The software behind it is open source, and so likely to be supported and developed beyond its current version and platforms. It's only on Windows, Mac, and Linux at the moment (though that's no small feat), but it can be made to run as a portable app, and its encryption standards—AES, Serpent, and Twofish—are supported by many other encryption apps that can work with it. In other words, TrueCrypt makes you feel better about taking all the revealing information about yourself or your work on the road. Check our guide to encrypting your data for more.
Computers, portable: Mozilla's desktop email client is an excellent tool for reading, sending, and archiving email, even if it doesn't get a ton of love these days—seeing as how seemingly everyone's doing their email thing on the web. But even if you don't use it as your main email client, Thunderbird remains the most reliable way to back up your email from any service and, in most cases, still access it when the web interface goes down. With the imminent release of Thunderbird 3, and the portable version to follow right after, Thunderbird might just turn a few more folks back to the idea of desktop email.
Computers, portable: They're not the same program, but they come from the same open-source roots. These instant messaging clients do the yeoman's work of connecting to all the major chat protocols and helping you maintain a universal buddy list. Pidgin does the job adequately, if without a ton of pizazz, on Windows and Linux clients (you can spice it up a bit with these snazzy plug-ins), while Adium, compiled from the same libpurple code library, is written with OS X's glassy looks in mind. Both are crucial if you don't want to run multiple memory-sucking IM clients on all your machines.
Computers, portable: Miro doesn't get enough love (here or elsewhere) for being a pretty great all-in-one aggregator for all the video on the web. The open-source video player handles video podcast feeds, Hulu streams (which you can subscribe to, show-by-show, TiVo-style), live streams, local files, and anything else with moving pictures with ease and grace, and you can take it wherever you go to ensure you can watch your favorite web-accessible or desktop videos.
Computers, portable: 7-Zip doesn't have the sexiest job on a computer, but since no two operating systems accept all the same compressed file formats, it's an essential download. It tackles the RAR files that file sharers are so fond of, makes sense of .tar and .gz files on Windows systems, and has its own compression format (.7z) that's space-saving and quick.
Computer, portable, and (coming soon on non-Maemo devices) mobile: Even if you don't think it's the absolute fastest or most cutting-edge browser, Firefox is safer than the well-known standard on most Windows systems, and it's customizable in every last detail. That makes it worth keeping on your USB drive as a go-to option for browsing at the in-laws or at home. With add-ons like Xmarks or Weave, it's also easy to keep your bookmarks—and keyword bookmark searches—within reach on any system. And when Firefox Mobile, a.k.a. Fennec, makes its debut on mobile phones, we might see some rather awesome synchronization of everything, right down to the last tab you had open at home.
Computers, web, mobile: Dropbox creates a single folder that you'll always be able to access, no matter where you are. That folder can actually sync files and folders from anywhere on your system, but the concept remains the same—instant backup for anything you drop in one location, across multiple computers, through Dropbox's web site, on the iPhone, and on mobile browsers. That makes it perfect for music you love to listen to, documents you need to work on, and photos you pick up at a relative's house. In other words, feel free to stop emailing yourself.
Computer, portable: Managing the multitude of codecs, formats, and restrictions on media files, from one system to another, is a pain you don't need. VLC Media player, installed on any system, just works. It's built with the goods to process, convert, resize, and stream just about any file you can find with audio or video, and its presence on a USB drive ensures nobody ever comes up embarrassed when their nephew's soccer video just won't play, even though, they swear, it worked just yesterday. For a guide on making the most of VLC's cross-codec powers, read Adam's tips on mastering your digital media with VLC.
These days, it only takes an increasingly-cheap USB thumb drive and a program like UNetbootin to create a portable Linux desktop you can run on any computer that can boot from a USB port. But check out the list of distributions UNetbootin can download and install—it's huge, and the names don't tell you much about which distro is best for on-the-go computing. Today we're detailing four no-install distributions—Damn Small Linux, Puppy Linux, Xubuntu, and Fedora—and helping you decide which might work for that spare thumb drive you've got lying around, or as just a part of your multi-gig monster stick. Read on for a four-way faceoff of bootable Linux systems. Note: All but one of the systems tested here were created with UNetbootin, available for Windows and Linux downloads, and using the latest version available that could boot from USB. All were run on the same laptop, a 2.0 gHz Centrino Duo ThinkPad with 2GB of memory/RAM. Fedora 9 was run using its own live USB creator, as explained previously. 
Ultra-small (and efficient) Linux distribution using an older version of the Linux kernel (great for real old hardware, not so hot for the newer stuff). 
This light bootable system can run from a USB stick, but if a system has more than 256MB of RAM, Puppy can move itself entirely onto a "ram disk," letting the user pull out their portable drive and keep working. Read Gina's walk-through of Puppy for details. 
Basically the Ubuntu platform, optimized to run the lighter Xfce desktop manager. 
The Fedora Project has its own handy, Windows-friendly Live USB maker that makes adding Fedora to your USB drive—without damaging your other data—pretty simple. Read our Fedora-on-a-stick guide for more info. 
So many video file formats, so many handheld video players, so many online video sites, and so little time. To have your favorite clips how you want them—whether that's on your DVR, iPod, PSP or desktop—you need the right utility to convert 'em into the format that works for you. Commercial video converter software's aplenty, but there are several solid free utilities that can convert your video files on every operating system, or if you've just got a web browser and a quick clip. Put DVDs on your iPod, YouTube videos on DVD, or convert any video file with today's top 10 free video rippers, encoders and converters.
Ok, so VLC is a media player, not converter, but if you're watching digital video, it's a must-have—plus VLC can indeed rip DVD's
Make your video files burnable to a DVD with Avi2Dvd, a utility that converts Avi/Ogm/Mkv/Wmv/Dvd files to Dvd/Svcd/Vcd format. Avi2Dvd can also produce DVD menus with chapter, audio, and subtitle buttons. 
Videora Converter is a set of programs, each designed to convert regular PC video files into a format tailored to your favorite video-playing handheld device. The Videora program list includes 
Convert almost all video formats including DivX, XviD, MOV, rm, rmvb, MPEG, VOB, DVD, WMV, AVI to MPEG-4 movie format for iPod/PSP or other portable video device, MP4 player or smart phone with Any Video Converter, which also supports user-defined video file formats as the output. Batch process multiple files that AVC saves to a pre-selected directory folder, leaving the original files untouched. 
Convert any video file to iPod-sized versions and automatically add the results to your iTunes library. iSquint is free, but Lifehacker readers have praised the pay-for iSquint upgrade, 
Putting any old video file - like the DivX/Xvid-encoded videos you've downloaded with BitTorrent - onto a DVD to play on your TV can be a daunting task. There's plenty of software that tackles this sort of thing for a price, but as a lover of open source software, free's always my first choice. 
The Video tab lets you set the format of your DVD player - namely whether your DVD should be NTSC or PAL-formatted. If you live in the US, NTSC is your pal. Most of Europe and Asia, on the other hand, use PAL. You can also set the encoding quality in the Encoding profile drop-down. If you feel that the quality of your authored DVDs isn't high enough, you might want to try upping the quality and ensuring the "Second encoding pass" checkbox is ticked. If you're more than happy with quality but you want to speed up the encoding process, you can lower the quality and get rid of the second encoding pass (you probably won't want to do this, but just in case, there it is).
DVD Flick is pretty no nonsense at this point; you can't build any fancy menu screens. Instead, the DVD you author and burn will simply play each file as a chapter in the order you add them to the project by default. If you want to add chapters to individual video files, select the video/title and click on Edit title... and change the method of chapter creation. You can create chapter points every so many minutes, create a set number of chapters per title, or leave your video chapter-free.
Before you start, pick the directory that the transcoded files will be saved to while DVD Flick works. You'll need to have a drive with a fair amount of space, so keep that in mind. You'll also want to keep that in mind so you can remove those files after the process is complete so you don't end up with a hard drive full of pre-burned DVDs.
Now that you've got everything set up how you want, click the button labeled 
