Lichess - The complete chess experience, play and compete in tournaments with friends others around the world.
DecodeChess - AI chess tutor and analysis
Chess Tempo Database - Chess Tempo Database gives you a library of more than 2 million searchable chess games.
ChessPad - ChessPad is a feature-rich chess game viewer and PGN file editor available for Windows.
Chess Insight - Chess Insight is a chess tutor that helps you with a number of analytical powers for judging every move in chess.
Scid vs. PC - Chess database and playing program.