An online organ that sounds like one
Most online instruments are a synthesiser with a picture on top. This one plays recordings of a real organ, so the attack, the tone and the decay are the instrument's own. The organ is the keyboard instrument that sustains: a chord stays as loud as long as you hold it.
A short history of the organ
The first organ, the hydraulis, was built in Alexandria in the 3rd century BC. The great church organs of the Baroque inspired Bach's music; the electric organs of the 20th century gave jazz, gospel and rock their sound.
From the keyboard to the real instrument
A real organ is written in treble and bass clef, plus a pedal staff on the pipe organ. The keyboard here plays the sounding notes, so a melody you find by ear is the melody you hear. To go further, the free sheet music and chord pages work with any instrument you can read music on.