Klevu - Klevu offers instant site search solution for eCommerce stores.

Google Custom Search - Google Custom Search enables you to create a search engine for your website, your blog, or a collection of websites.

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.

Swiftype Site Search - Swiftype Site Search helps to sell more, get the right answer to more people on the platform and surface relevant content for readers and followers.

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.

Hawk Search - Site-search engine for eCommerce platforms.