A portable app is a computer program that you can carry around with you on a USB flash drive (a "stick") and use on any Windows computer. When your stick is plugged in, you have access to your software and personal data just as you would on your own PC. And when you unplug the device, none of your personal data is left behind on the PC.
Most of these applications have been developed as Open Source Software, free to use and modify under the GNU license. Most of these projects accept donations to help support the efforts of programmers and overhead of developing and hosting them on the internet.
app-stick.com