Site official: http://chessok.com/?page_id=145

ALL THE DATA (from the official site):

Windows OS	iOS	Android OS	Web Interface

• Play with customizable time controls, including freestyle.
• Find opponents by playing strength, time control, game type (friendly/rated);
• Play in daily prize tournaments for free - individual, team and mixed (individual and team) tournaments are held regularly.
• Create or join a team and fight your way into the League Tournaments.
• Follow free online broadcasts of super tournaments and best matches;
• Use online game database and computer analysis;
• Give or take chess lessons;
• Discuss latest chess news in chat;
• Buy a one-year Membership at ChessOK Playing Zone (log in using your Playing Zone username), and gain full membership rights for only $18 / €14!
• Buy any of our Aquarium products and gain one-year membership for free! The Aquarium software is an advanced yet friendly tool you may - among other things - use to store and further analyze the games you play in the ChessOK Playing Zone. (NOTE: Please provide your ChessOK Playing Zone username in the Comments textbox on Order Confirmation)
• New! Use our new apps for iPhone/iPad and Android OS to play wherever you want!