The top half of the screen is a classic, 16 step pattern grid. For each sample, you can change the filter frequency & resonance.
Create your pattern or, if you feel lazy, just press the "randomize" button and enjoy!
The bottom half is an 8 bit style, lo-fi synth. Click on the little piano-keys or use the computer keyboard to play.
Oh, and there is a filter too. :-)
NEW: on Chrome, you can also use a MIDI keyboard connected to your computer - and you really should :-)