Jolicloud is currently at closed alpha testing stage and only offer download on an invitation basis.
The download is a LiveCD installer of around 600MB, distributed in iso format. One shall have to use a USB creator software to mount the iso file on a USB drive before it can be installed on a PC.
This OS based on Ubuntu Netbook Remix
The Jolicloud Manifesto
At Jolicloud we believe a movement has started. A movement that will change the computer industry forever: a world where computers are inexpensive, where operating systems are free and software is online. This is the world we dreamed of when we first discovered computers and the Internet. And this is why we wanted to build an operating system (OS) around a platform that gives everyone the opportunity to be part of this movement and access a whole new range of possibilities.