Kingdom Sostis is a tower defense game set in a medieval and magical world. It challenges the player in 10 battles of gradually increasing difficulty fought to preserve the kingdom's freedom.
Extract the zip file. Run "Kingdom Sostsis.x86" if you are on a 32-bit system or "Kingdom Sostis.x86_64" if you are on a 64-bit system. You might also need to permit your system to execute those files as programs. On Ubuntu, right click on the file, properties, permissions, allow executing file as program.