The free app at www.thebrain.com already has a .zip format installer. I don't know how to make that into a portable app, but I would really appreciate it if someone could do so.
Pros:
It's free (but you can activate the pro version)
It runs on USB drives now via its .zip version
Cons:
It requires a .brain file, and I don't know how one would specify where to store the brain folder on the USB drive.
Please make my year and let me put this app in the PortableApps launcher.
Thanks!
missed something on thebrain website, but it seems to be fairly simliar to this:
https://portableapps.com/node/10952 which is Freemind, a mind mapping application,
featured at this site.