Lichess.org

Lichess is an entirely free, no ads, no paywalls, open-source chess website.

Ran by a charity made up of the chess and tech community, made for the community, millions of players use Lichess to play, study and learn chess.

Features include multiple chess formats, unlimited puzzles, opening books, endgame tablebases, hundreds of thousands of online opponents at any time, bot opponents, insights to help you learn from your own mistakes and weaknesses, learning tools, and much more - all entirely for free, powered by donations and community support.