Deepolis is an underwater MMO game. Pilot your submarine into the depths, to battle monsters and other submarine clans. Wreckage can be salvaged to sell at underwater stations, to upgrade your craft and complete harder quests.
Deepolis plays from your browser, with no installation required. You have to register for an account, choose one of three factions to join, then you're off. To start with, you have to complete training quests, teaching you movement and combat. It's all mouse controlled, and combat is just a case of clicking a target and choosing a weapon. Your survival depends on you having higher stats than your opponent.
While the game has three dimensions, it's not presented in true 3D, which can be a bit disconcerting to begin with. Sound is fairly generic too. Despite this, if you like the idea of underwater questing, Deepolis has lots of users, and feels well populated. There are paid options in Deepolis, meaning free users will have to work that much harder to keep an income so they can buy better weaponry and subs.
While it doesn't look amazing, Deepolis is an reasonable MMO for fans of the genre, and is that much easier to play for not needing installation.