Get better at the opening with Chess Openings Pro and its collection of more than 10000 openings and its database of over 2 million Grandmaster games.

It also helps you find which chess openings are better by showing you their respective win rates.
For example did you know that black wins 4% more games on average by answering "1. e4" with the Sicilian Defence ("c5") rather than an Open Game ("e5")?