Typesense - Typo tolerant, delightfully simple, open source search 🔍
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.
Expertrec - Adds super fast search autocomplete, spell correct and search listing pages to your site search.
Appbase.io - Search stack for building modern apps
Sajari - Sajari is a machine learning powered search and matching service.
Reactive Search - UI components for building Amazon / Yelp like Search