FolkTuneFinder is a search engine for folk tunes.
If you know how the tune starts, use the keyboard or contour search. You can filter to narrow down your search results. Or you can just browse tunes without having to search.
Type in the title of a tune
If you're looking for a tune and you know the melody, type in some notes from the start, at least 5.
If the idea of typing something into a keyboard isn't your thing, try contour search.
Describe your tune in terms of ups and downs, and same note repeated. Type as much in as you know from the start of the tune. Also known as Parsons code.