Datamuse is a collection of free websites, mobile apps, and APIs designed to help people create and communicate more effectively.

OneLook® is the Web's premier search engine for English words, indexing 10 million unique words and phrases in more than 1000 dictionaries and glossaries. More than a million unique users visit OneLook every month. The OneLook Thesaurus and Google Docs extension are brainstorming tools affiliated with the site.

RhymeZone is the premier tool for creative writers of all kinds, combining the features of a rhyming dictionary and a thesaurus. It answers more than 30 million queries from several million unique users every month. Rimar.io is its new Spanish sibling.

The Datamuse API is a lexical search service for developers. It's answering ... queries per second right now from hundreds of applications.