Filler
I've been playing Filler for the past few days and despite it's simplicity, I'm still having fun. The objective is simple enough, fill in 2/3 of the box with your balls and you get to move on. Get hit by the balls flying around and you lose a life. Lose too many lives and it's game over.
To play, hold down the left mouse button. A 'filler ball' will begin to expand at that point until you let go of the button. Don't get hit by the 'flying balls' (ever play jezzball or qiz?). You can move your filler ball around by moving the mouse around while it is expanding.
If your filler ball hits another filler, it will stop growing. Walls do not stop the growth, while the flying balls kill it off. (I think the flying balls hit the filler balls too soon. It can be very frustrating, so err on the side of caution.) Once the filler ball is finished (you let it go), it will drop down to the bottom of the screen. The filler balls are not static and will bounce around, or be pushed off to the side. It's very hard to build up a 'wall' that you can work behind. It can be done, but it's not easy and it really isn't worth trying since the wall will just fall down a few moments later anyways.
Another tactic may be to just build hundreds of small filler balls until you get to the 66.6% mark, but you only have a limited number of filler balls to make. Once you run out, the game is not over, but you lose a life for every ball you create from that point on, so it's not a great strategy.
Instead, try to make your filler balls as big as you can when you can. Smaller filler balls can be used later on in each level to fill up those spaces, or just to make room. A great strategy is to work in the upper corners. Create a ball, let it drop away and then start making a new one. The first one you built will act as a shield allowing you to build the second one. As long as you wait a moment for the first one to start dropping away, you should be fine.
Play Filler at Kongregate.