Mass Defense is an interesting multi-platform game. It is an Opera widget, so it should work on any platform that supports Opera browser. The game is basically about defending a planet against other objects. Your only weapon to defend the planet is a gun that shoots round projectiles. When those projectiles hit incoming objects, their trajectory is changed. When an object hits your planet, your health decreases, and when you run out of health, the game will be over. Now, the description of the game is that it is a physics-based action game. But in all honesty, there is no way that the physics behind the game are realistic, at all. That's not an issue though, since the game is fun. As you progress through it, more and more objects will be on the screen at the same time, and they will be bigger. The difficulty also arises when you can't shoot at objects that are behind other objects. Ideally, those planets, comets, or whatever they are would crash with each other as well, but that doesn't happen in the game. So you have to be very careful in conserving ammo and only firing at those objects that are really close to you.
I thought that the original size of the game was a bit small, so I increased the zoom to 200%, and that looked good enough. The only problem that I had with the game was that at times, when I was shooting, the window would disappear and I would have to click the dock icon to bring it back up.