The tagline is a bit confusing. Saying a movie is “on” a website strongly implies the film is directly watchable on that site (e.g. “best films on Netflix this month”). So at first I thought maybe this was perhaps about the best illustrative video clips uploaded to Wikipedia, or public domain films.
A clearer description might be “Discover the best movies through Wikipedia” or “via Wikipedia”. Or perhaps some like “Using Wikipedia to discover the best movies”.