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Bart Bonte is a Belgian programmer who produces charming little games without much in the way of instructions; the idea is to discover the rules for yourself. In this (click the image or here) you are presented with various screens. In the one pictured you click on the purple duck to advance to the next level. But I leave you to discover the game's other secrets.
Bonte's website here. He reminds me of the even-more-whimsical Ferry Halim.
Warning: SFX and music -- the latter can be muted with a button at upper left.