SolEol searches for subtitles for your movies by using a unique "electronic signature" (also called a "hash") on your files (downloaded or otherwise) and searches OpenSubtitles' massive database for matching results in your chosen language(s).
The application supports drag-and-drop, automated operation, and includes a basic CLI for automations. It also allows users to upload their own subtitles, be they obtained elsewhere or made from scratch, to share with the community and benefit people with similar needs.
The application is feature-complete. Donation link available within application, in case you find it useful.