Bug Hunter - the secret of Algebra.
You choose an avatar for the game and you travel from planet to planet "hunting and capturing" bugs. Your space ship goes to the first planet (the blue and purple one) to work your way through the 20 levels. Each level introduces a skill and starts with only bugs.
You cannot unlock a level until you've completed the level before. If you do a good job, you can get up to three stars depending how well you accomplish your goal. Every level you complete unlocks the next level.
At various points you receive instructions on what you do next. Each set of instructions builds on what you've been doing. You do not always capture bugs because they do introduce variables and constants in addition to the bugs.
If you look at the picture to the left, it is from the second planet. Notice how you have a left side and a right side with a pathway inbetween. Right now, the red middle indicates I cannot drag anything across, I have to do the opposite to both sides with the button on the bottom.
It slowly builds algebraic skills one step at a time. I will admit, I am visiting the second planet out of five and I'm enjoying it tremendously. I plan to reach the end of the fifth planet before I head off traveling. I think students who need scaffolding will enjoy this to help them gain algebraic skills.
The best thing about this app? Its free. You get more than just a sampling, it seems to be a full app with a lot of questions. Check it out, give it a try.