QuickSearch keeps a SQLite/FTS5 index of the directories you choose and searches them by both filename and file content. It extracts text from documents, PDFs, archives and office files, watches the indexed paths for changes and reindexes in the background while the application is open.
The same binary doubles as a terminal search tool: "quicksearch" followed by search terms prints ranked results and exits without starting the indexer, the file watcher or any background thread.