The PortableApps collection of open source programs runs from any USB drive and comes with its own launcher and organizer.
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The real beauty of technology is when it's being used for things its makers never foresaw. As William Gibson once put it, "The street finds its own uses for things."
This definitely goes for the ways USB thumb drives can be used. The most obvious stuff is self-evident: take work with you, make backups to it, and so on. But there's a whole galaxy of other possibilities, and I've compiled many of the most useful ones here. Some will almost certainly be familiar; others will be new to you. All of them are worth knowing about, and almost all are worth trying at least once.
Note that some of these tips won't work unless your system supports booting from a USB device. Not all computers do. Sometimes this can be addressed through a BIOS upgrade, but not always, so test before attempting anything crucial.
1. Take Your Programs With You
If you're going to take your data for a ride, why not take your programs along with you, too? Most people have heard about the concept of running applications from a USB drive, but get hung up on the details. Thankfully, there are prepackaged ways to do this, so the choice of apps and the deployment are all done for you.
U3 Smart Drives are the most common commercial way to do this, but I've typically avoided that in favor of noncommercial solutions.
The single best repository for free applications that can live on a thumb drive is PortableApps, a large and continually growing collection of liberally licensed open-source programs in almost any category. Many of them are high-quality substitutes for existing commercial applications: the OpenOffice.org suite (version 3 is available as a release candidate for PortableApps), Firefox, and Thunderbird; the InfraRecorder CD/DVD burning app; and tons more.
The whole suite is controlled with a tray-based launching application (also open source), and the apps themselves are repackaged with an installer that's thoroughly documented -- anyone can package an app as a PortableApp as long as they follow the directions. Programs and user data are kept separate from each other and can be managed independently. Example: If you upgrade to a new version of Pidgin, your chat logs for that program are not erased.
While it's easiest to use apps written specifically for the PortableApps suite, any application that can run in a standalone directory without needing a formal install will work -- and it will show up in the PortableApps launcher automatically, too. If the apps don't appear, Select "Options | Refresh App Icons" from the launcher's menu to force them to show up.
The apps in PortableApps are typically open source, but the community that's formed around the suite has informal hints for running many proprietary applications, like Skype, in a portable fashion. Brave early adopters also can check out the application development forum and try early editions of new portable programs -- e.g., Google Chrome.
Another collection of programs along the same lines as PortableApps is winPenPack, available in both English and Italian versions and packed with its own tray-launcher application, too.
One final product that deserves mention here is MojoPac, a commercial application that performs software virtualization. Install it on a USB device and you can run a self-contained Windows user instance from that device, which includes applications that normally can't be installed directly to a USB drive (such as Microsoft Office). The host computer isn't touched at all, and in fact the MojoPac user can't do anything to the host computer even if he wants to. Right now the program mainly supports Windows XP, but Vista support is under way.