The open source app Concrete5 looks like a great thing to make portable, since it is so much easier to use than other web editors. It's from Sourceforge, so it's also open source and free, making it a great candidate. I think this could be a really great app.
Link please
PortableApps.com Advocate
As it is PHP/MySQL-Based (plus PEAR PHP extensions), it should be possible to use it with Xampp?! (Didn't try it, though). Look here: https://portableapps.com/apps/development/xampp
You should be able to install concrete5 over it.
http://www.concrete5.org/
Looks quite cool, btw!