I find the key-and-scale-locked piano keyboard in Korg Gadget iPad app very nice for instant tune-making (since I don't know musical theory worth squat).
It would be nice if the typing keyboard supported the same sort of thing, i.e. constraining the rows into a given scale, key, octave range and offset.
Crudely spliced-together screenshot showing all the scale choices in Gadget:
And the effects of choosing different options:
Scale-and-key-locked keyboard piano
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Scale-and-key-locked keyboard piano
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