JonDo (formaly known as JAP, Java Anon Proxy) from the company JonDos is an open source anonymity tool invented by a german university. It sends your traffic encrypted through different "mixes" so that absolutely nobody, not even the owner of on of the mixes know who is accessing which site.
It works similar to the more open TOR system. This is also on of the best tools to circumvent censorship. Just follow the installation instructions on installing the Java client available for Windows, Unix/Linux, MacOS and others. As many other local proxytools like hopster or HTTPort you have to run the program and enter in your browser the proxy IP 127.0.0.1 (for your local PC) and the port 4001 for the JonDonym software.
Several mixes are free to use, however there are also some mixes where you have to pay for.