Imagine if, rather than relying on the proprietary software of a large professional search engine operator, your search engine was run by many private computers which aren't under the control of any one company or individual. Well, that's what YaCy does! The resulting decentralized web search currently has about 1.4 billion documents in its index (and growing - download and install YaCy to help out!) and more than 600 peer operators contribute each month. About 130,000 search queries are performed with this network each day.
Live image of the 'freeworld' network
Installation is easy!
The installation takes only three minutes. Just download the release, decompress the package and run the start script. On linux you need OpenJDK7. You don't need to install external databases or a web server, everything is already included in YaCy.