Everything by Voidtools - Everything. Locate files and folders by name instantly. Everything. Small installation file. Clean and simple user interface.
Meta Search - Search your Desktop, Google Drive, Dropbox, Gmail, Evernote.
DocFetcher - DocFetcher is a portable German/English open source desktop search application.
Vaultedge - Access all your documents in one place.
Recoll - Recoll is a desktop full-text search tool. Recoll finds keywords inside documents as well as file names.
Google Cloud Search - Search across all your company's content in G Suite.