A couple of people have written and asked me to mention Portable Apps. PortableApps.com is the most well-known source for portable software, but there are many more programs that will run on a USB thumb drive. Many programs will even run from a thumb drive with little or no modification, for example, Skype on linux (and possibly on Windows too).
Portable Apps as offered by PortableApps.com are Windows programs that you can put on a USB thumb drive (or on any kind of storage device) that will run without needing to install them on the computer. The advantages to this are:
I recently followed some instructions for putting Damn Small Linux on a thumb drive and was suprised to find that the latest version easily boots inside of Windows and Linux as well as directly from the thumb drive.
Here are some screenshots of Damn Small Linux running inside of Ubuntu Linux. Notice the window borders:
Many people have expressed interest about portable apps for Linux. There are also a good selection of portable apps available for Mac OS X. You can probably find others in this excellent list from Wikipedia.
Portable apps will not really provide security against an infected public computer. They may actually reduce your security on public computers for the following reasons:
Many people have heard of Portable Apps and are probably wondering if they will run on Linux. Portable Apps (as distributed by PortableApps.com) are not made to run on Linux, but I have been able to get them to work on Linux under WINE.
Here is a screenshot of a couple of the Windows versions of Portable Apps running on Ubuntu Linux from a USB thumb drive:
If you make web sites, you may be interested in the new portable web servers that are available. You can run Apache, PHP, MySQL and other tools from a USB thumb drive.
There is another portable webserver called WOS Portable that includes Apache, PHP (4 and 5), MySQL, ImageMagick, and the Typo3 content management system. The "WOS" is for "webserver on a stick".