Keyspider.io - Keyspider is a cloud-based search platform that provides the best search experiences for users across your Websites, Ecommerce, Services, and Workplace.
Algolia - Algolia's Search API makes it easy to deliver a great search experience in your apps & websites. Algolia Search provides hosted full-text, numerical, faceted and geolocalized search.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.
Algolia Search for WordPress - Bring instant and relevant search to your WordPress blog
Site Search 360 - Site Search 360 enhances and improves your built-in CMS or product search with autocompletion, semantic search, filters, facets, detailed analytics, and a whole lot of customization options.
SearchWP for Firefox - Jump-to-word buttons and highlighting for the search box content