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Atomic Chaos (a.k.a. Kaos) is a Rotational/Sequential puzzle invented by Christoph Hausammann in 1990. 

It has six half-filled tubes with colored balls. The version I have is comprised by one back ball, two whites, three green, four red, five blue and six yellow. There's at least another version with different color arrangements, like six red balls instead of six yellow.

The goal here is to scramble the puzzle by tilting the tubes right or left and rotate it at the middle to join tubes with different lengths, thus getting different colored balls in the same tube. When you have scrambled it, the most efficient technique is to use a sequential type of movements to get the balls back into their correspondent tube. You can start by tilting the puzzle to one of its sides and join the longest tube with the shortest. Now just rotate it, clockwise or counterclockwise depending on the side you tilted the puzzle, and you can see the balls falling one by one to each tube. Try to restore first, the longest tube with its respective balls and lastly, the shortest one.

It's not a very difficult puzzle, although a bit tedious to solve. Once you get how it's supposed to be solved, it's just a matter of time, due to its nature of sequential movements. It's more fun to scramble, though :-p ... The Tower of Hanoi, the Spin Out or even the Olympic Wander Rings are puzzles of similar difficulty, where you have to perform a sequence of movements to solve them. 

They're quite rare to find these days, but as of the time of writing, there's still a few for sale here.

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