With the proliferation of USB thumb drives, the practice of using software from portable devices has gained considerable momentum. As such, you now have sites like PortableApps and PenDriveApps, among others.
By its purest definition, for an application to be portable, you must be able to run it from a portable device, leaving no traces of its presence on the host system, once you're done. This protects privacy, maintains system integrity and also hides your tracks, if you are so inclined.
While I understand the benefits and need to classify software in such a manner, I'm not as picky. I've been using PC's since the days of DOS and remember when you simply ran a program from it's folder and deleted it in order to "uninstall" it. Even in the early days of Windows, you didn't need to worry about drivers being added to your System directories, Registry entries being created, library files being registered, and so forth. That's where Apple has things right. In order to rid your computer of a particular program, you simply drag it to the trash and it's uninstalled. That is not the case with Windows. A large percentage of programs are very intrusive, with some requiring installation in order to work and that annoys me.
So, I've always kept a large collection of Freeware that allows me to run the applications from anywhere, without needing to worry about installation. In fact, when I reinstall Windows, one of the steps I take is to copy all these applications to a separate location, so that I can simply move them back when I'm done.
With the size of storage available on thumb drives now, I have taken this one step further and essentially created a portable PC of my own, by copying these applications to my favourite USB drive, for easy accessibility. The one program I can't live without is Total Commander. It's one of the only pieces of Shareware I've ever kept and yes, I've even registered it. Mr. Ghisler deserves to be paid for this incredibly powerful program.
I've customized my version to an extreme, creating a large number of toolbars that include access to all of the programs I use on a frequent basis. Total Commander is even designed with portability in mind, in that it uses environment variables such as %COMMANDER_PATH% and %COMMANDER_DRIVE% to help you run programs from relative paths, such as a dynamically changing removable drive, rather than explicit locations, such as the C: drive.
A lot of the programs I launch from this drive leave traces of their existence behind on host systems, such as registry entries or configuration files, usually located in the user AppData directories. In that sense, the programs are not truly portable. They are however, able to run easily from any location, without complex installations, making them faster and easier to use and that's the only thing thing about which I'm concerned.
With only a couple exceptions, the majority of these programs run comfortably from any drive, without special configurations. Those that don't are marked accordingly, in the list below. All of them take up less than 2GB of space and make for one very powerful suite of applications.