If you're looking for a free alternative to Mac OS or Windows 7 you could choose Ubuntu Linux
Alternatively you might fancy a version of Linux that comes with a bunch of preloaded hacking tools. If that's your cup of tea - and honestly we have to wonder about your motives - then your every wish has been fulfilled by the hacker collective known as Anonymous.
The link to the software is/was here
but please, we beg you, don't do it.
The very idea of Anonymous-OS sounds like a nightmare. These are people who take control of computers and networks for fun so the idea of installing an Operating System prepared by them should sound alarm bells.
It comes as no surprise that the news wires are full of reports that Anonymous-OS is riddled with the Zeus Trojan, and the simple thought is to say 'well what did you expect?'.
Sophos has a slightly more sophisticated view
but the upshot is that you'd be crazy to use the software even though it doesn't appear to carry a Malware payload.
There have been suggestions that Anonymous OS (or the tools that are included) could be a literal Trojan Horse that reports user information to the Police, FBI or some other law enforcement agency.
I wouldn't want to argue about entrapment or probable cause or any other niceties. My guess is that the first question would be 'Why did you download Anonymous OS?' and from that point onward you would be absolutely screwed.