What are some alternatives?
When comparing IMDb and Letterboxd, you can also consider the following products
Simkl - Simkl is a TV, anime, and movie tracker that keeps a history of all the shows and movies you watch in one, central location. It’s a mobile app, a website, Google Chrome extension to keep track of everything you watch and integrates with many TV apps
Trakt.tv - Automatically track TV shows & movies you're watching.
Rotten Tomatoes - Rotten Tomatoes, home of the Tomatometer, is the most trusted measurement of quality for Movies & TV. The definitive site for Reviews, Trailers, Showtimes, and Tickets
Metacritic - Metacritic aggregates music, game, tv, and movie reviews from the leading critics. Only Metacritic.com uses METASCORES, which let you know at a glance how each item was reviewed.
themoviedb.org - free movie database
Criticker - The TCI is a measure of the similarity between two people's taste in films.