Roll20 - Roll20 is a suite of easy-to-use digital tools that expand pen-and-paper gameplay.
Chess Tempo Database - Chess Tempo Database gives you a library of more than 2 million searchable chess games.
GOG.com - DRM-free game store, selling both new and old titles. No clients required.
DecodeChess - AI chess tutor and analysis
Diep.io - Diep.io is a multiplayer action game available for web browsers, Android, and iOS, created by Brazilian developer Matheus Valadares. Players control tanks and earn points by destroying shapes and killing other players in a 2D arena.
ChessPad - ChessPad is a feature-rich chess game viewer and PGN file editor available for Windows.