I'm presenting an app which isn't open source, but I thought it would be cool to have it portable. Scratch (https://www.scratch.mit.edu) is a block based programming language, so you put parts together to create a Programm. But I don't want to talk too much about it, here it is:
Download ScratchDesktopPortable_7.6.paf.exe (101.3mb / 252mb installed)
Once installed in Portable Apps, windows Security identifies the installed exe as containing a "Severe issue".