Click on the link above, I will say its a very nice online musical instrument, that let you easily create some rhythms just by clicking on the rectangle boxes.
The rhythm will actually run from left to right, column by column according to which boxes you have activate, similar to a musical box. Boxes at lower position/row will produce lower frequency note, just like a musical box.
Below is the video of one of my trial in creating my own rhythm, hope you’ll like it (sorry about the quality).
Try your now!