LUNR.js - A bit like Solr, but much smaller and not as bright

Lunr.js is a small, full-text search library for use in the browser. It indexes JSON documents and provides a simple search interface for retrieving documents that best match text queries. A bit like Solr, but much smaller and not as bright. Lunr enables you to provide a great search experience without the need for external, server-side, search services. Lunr has no external dependencies and works in your browser or on the server with node.js.

For web applications with all their data already sitting in the client, it makes sense to be able to search that data on the client too. A local search index will be quicker, there is no network overhead, and will remain available and usable even without a network connection.