Waveboard looks basically identical to Mellotron, I won't put a picture
of it here. It essentially does exactly what Mellotron does, but rather
than looping every instrument's sounds, it plays them once, when a key
is struck. This is useful for instruments that don't sustain
infinitely, like pianos, guitars, and drumsets. Likewise, Mellotron is
better suited for organs, synthesizers, flutes, and string instruments.
You are also able to define your own instruments in Waveboard just as
you could with Mellotron.