TouchKeys Multi-Touch Musical Keyboard by Andrew McPherson is a controller overlay that allows to track the finger position on the key – the one I ever wanted. Since this is a Kickstarter project it is not yet available but you could do it..
but it’s for large Keys, not for mini sized ones (Microkorgm etc) – I wish this feature would be standard on all keyboards on the world and freely assignable. these send MIDI Controllers via USB. And it’s open source. The kits are assembled or DIY for your controller. – they don’t offer 37 keys .. so far. But this is another cool approach – I don’t know how it feels to play those glued onto the keys, but it is what I’d like to have. there’s 3 solutions so far: Vibe Bar (a controller mounted unterneath the keyboard, so it’s not exaclty IT) and endeavour which has larger keys than normal keyboards.