If you want a portable Ubuntu, “Portable Ubuntu Remix” is for you. It is an Ubuntu system running as a Windows application.
Now there are N reasons why you would need something like this.
1. If you want to try out Ubuntu in a really simple way, if you are new to Virtualbox, VMWare.
2. If you really need to run some Linux / Ubuntu applications in Windows, full blow app apart from cygwin.
3. As a replacement to Virtualization. This is in fact faster than Virtualized solution.
4. And of course, since it’s portable, you can take it anywhere with you on a Pendrive, etc.
Unfortunately, Portable Ubuntu Remix only works on Windows 32bit.
Note: The credentials are — user: pubuntu password:123456.