Portable apps aren't anything new. There are variations of "single executable apps" for most platforms, and some people swear by keeping their own applications with them for use when away from home. I don't usually do that, as most of what I do is on-line, but there is one exception: security.

When I'm asked to help a Windows user figure out what is wrong with his or her computer, I generally take a USB drive and nothing else. I also usually run dd on that Flash drive when I get back home, because Windows can be a breeding ground for nasty infections. In order to build a USB device quickly that I can use to help my Windows friends, I like to use the awesome open-source program at http://portableapps.com.

The downloadable program provides a sort of "app store" for downloading individual portable apps. It makes sure all of your apps are up to date, and it's a great way to browse the different categories and look for apps that might be useful. Granted, many of the portable apps themselves aren't open source, but the program that manages them for you is. If you ever need to help friends or acquaintances with their infected systems, a USB drive prepped with the Windows-based portableapps.com application is a great way to start.