Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
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.
ClassicPress - The WordPress fork. No Gutenberg. Great future!
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.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
ElasticSearch - Elasticsearch is an open source, distributed, RESTful search engine.