Slidercrash comes from Joachim Merten. It's got some interesting elements.
First, you must crash the reds together, and the blues etc. Look at the first image. See the top red circle? There's a ring around it. That means it can't move on its own. It can be crashed into and then travel.
There are 60 levels altogether. I got stuck on Rookie #2! I really like this game! Hey, it's free too.
Actually, you get 15 free tutorial & 15 Rookie levels. I was happy to pay $.99 for the next 30 levels. Right now I've solved 46 of the 60 puzzles.
Slidercrash is definitely worth your time.