Dooble partially integrates the distributed search engine YaCy.
IceCat could do this to - Read about YaCy, distributed under GPLv2+
From https://en.wikipedia.org/wiki/YaCy
YaCy (pronounced "ya see") is a free distributed search engine,
built on principles of peer-to-peer (P2P) networks.[1][2]
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.
Compared to semi-distributed search engines, the YaCy-network has
a decentralised 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 his or her computer. (Several mechanisms
are provided to protect the user's privacy.)
Access to the search functions is made by a locally running web
server which provides a search box to enter search terms, and
returns search results in a similar format to other popular search
engines.