YaCy

YaCy (pronounced “ya see”) is a free distributed search engine built on the principles of peer-to-peer (P2P) networks, created by Michael Christen in 2003. The engine is written in Java and distributed on several hundred computers, as of September 2006, so-called YaCy-peers. Each YaCy-peer independently crawls through the Internet, analyzes and indexes found web pages, and stores indexing results in a common database (so-called index) which is shared with other YaCy-peers using principles of peer-to-peer. It is a search engine that everyone can use to build a search portal for their intranet and to help search the public internet.

Compared to semi-distributed search engines, the YaCy network has a distributed architecture. All YaCy-peers are equal and no central server exists. It can be run either in a crawling mode or as a local proxy server, indexing web pages visited by the person running YaCy on their computer. Several mechanisms are provided to protect the user's privacy. Access to the search functions is made by a locally run web server which provides a search box to enter search terms, and returns search results in a similar format to other popular search engines.