YaCy (pronounced “ya see”) is a free distributed search engine, built on principles of peer-to-peer (P2P) networks. Its core is a computer program written in Java 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 P2P networks. It is a free search engine that everyone can use to build a search portal for their intranet and to help search the public internet clearly.
Anyone can have 100% control over it. And run it locally. Thus, it is trade-free.