World of Sea Battle is an indie open-world naval action game with RPG and simulator elements, developed by Thera Interactive. While it features open-world and multiplayer tags, the lack of wide recognition, a major publisher, and mainstream coverage suggests a small but steady niche community. Its indie studio background and limited marketing mean the player base is likely in the low hundreds daily. I do not classify this as a true MMO as there's no clear indication of massive concurrent player interactions.