Also on Quora - What is better, a custom Google search or Algolia?
- Elasticsearch, Lucene, Solr
- Google custom search
How does it compare to search engines with web crawlers?
- lunr, elasticlunr
RDBMS and NoSQL's built-in?
- SQLite FTS4, FTS5
- PostGres plugin
Or, some other implementations, like Python's Whoosh?