Stba.io is an awesome war game. There are two teams red and blue and you join one of them. Before you join the game you should choose a unit, it could be a tank or a spaceship or something else. Each unit has pros and cons and has individual characteristics such as speed, attack, dps, range.
Try each of them and find the best one for you. After you made a choice your unit will spawn on the map where goes battle. Your goal is to destroy opponents base, so you better kill enemies before. This game very addictive, try it!