Try out the Harmonic Table

Try it on screen

On screen is obviously not the same as touching real keys, however this demo.
(click to play) does give you an idea of how adjacent notes sound good together. [Try it out]

Try it on iPad

• SkyLight's - Hex Osc
  
• Somascape's HexaChrom.
• Shiverware's Musix.

Try it on Android

• Tuning Bell's IsoKeys™.