I have a U3 Cruzer Flash Drive (also known as a Pen Drive.) and I am capable of running programs such as FireFox, Opera, OperaTor, EssentialPIM, uTorrent, just to name a few.
I am using Lupo PenSuite. Lupo Pensuite (Full Edition) comes with many useful applications.
It includes 2 web browsers. FireFox and Opera. 2 email clients. ThunderBird and unPOPuk.
2 instant messengers. Miranda and PixaMSN. Lupo is fully customize-able. It has 6 or 7 themes. Thats is just the start of everything. You can also add apps from PortableApps.com and PortableFreeware.com.