Lichess - The complete chess experience, play and compete in tournaments with friends others around the world.
ChessDB - ChessDB - a free Chess database for Mac OS X, Windows, Linux, and UNIX - like ChessBase, but better
Chess.com - Play chess on Chess.
DecodeChess - AI chess tutor and analysis
Fritz - Fritz is the world’s most popular chess program, developed by ChessBase, “the world's leading...
Chess Tempo Database - Chess Tempo Database gives you a library of more than 2 million searchable chess games.