Freeplane (http://freeplane.sourceforge.net/wiki/index.php/Main_Page) is a mindmappingtool like Freemind and already available as portableapp: https://sourceforge.net/projects/freeplane/files/freeplane%20stable/
It also works fine with the portableapps platform. (Tested by myself.)
And the headdeveloper of Freeplane (Dimitry Polivaev) himself has already offered his tool for portableapps: https://portableapps.com/node/34224
So, ... take it!
I like applications like this, except I've no idea what to do with them except pleay. maybe I am too old
Wm