Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Wikipedia - Wikipedia is a free online encyclopedia, created and edited by volunteers around the world and hosted by the Wikimedia Foundation.
PIPL Professional People Search Engine - PIPL professional search is used to find the person behind an email,phone or social profile and covers over 3 Billion people worldwide.
Miraheze - Miraheze is a wiki farm (hosts wikis) for free and with no ads, it also provides custom domains...
WikiGalaxy - Explore wikipedia in 3d
Kiwix - Kiwix enables you to have the whole Wikipedia at hand wherever you go!