Square Enix is celebrating the 10th anniversary of Kingdom Hearts with their first free to play browser game called Kingdom Hearts X Chi. The player can travel to different Disney worlds and battles are done though a strategic card game. Items can be earned and unlocked, or you can pay to get them sooner, which is common to the free to play business model.
According to SE’s Kingdom Hearts site, the game will require a PC to play. Not sure if that explicitly means Windows only or if it may also be playable on Mac and Linux. Furthermore, the title has only been announced in Japan without an actual release date.