Because it's Easter, I'll be a little bit more helpful. Try to read and understand this. The name "Unix" properly refers to AT&T’s original UNIX operating system, which is not free. However, when people say "Unix" they’re usually referring to a whole group of similar operating systems, many of which are free. So try to understand what you want. There are some which are descended from Unix such as: FreeBSD, NetBSD, OpenBSD, and Solaris. Also Mac OS X is descended from "true" UNIX but is not free and does not have a live CD. Others are more "Unix-like" and Linux is the most well-known one. Linux is not based on the original UNIX code at all, but it was written to follow the same principles.
FreeBSD found at
http://www.freebsd.org/ (best for use on PC hardware)
NetBSD found at
http://www.netbsd.org/ (good for use on nearly any hardware)
OpenBSD found at
http://www.openbsd.org/ (excellent for security, ideal for servers)
OpenIndiana port of Solaris found at
http://openindiana.org/ (robust, complex, commercial-grade system)
Still 2 hits left. Use them wisely.