Arduino based palmtop

I once owned a Palmtop which I found very useful. It kept my address book and diary, and I like the stylus writing screen. I still have several palms, but the batteries are dying, and I do not have interfaces to modern operating systems.

I would like to build a touch screen palm top powered by a Raspberry Pi.

My questions are:

Has anyone done this before? If so please provide links.

If I decide to crowd fund larger scale production of an Arduino based palmtop, I will want to have an input writing like graffiti. How can I ensure that my input script is different enough that I do not get legally attacked by Palm or Xerox?

I can't work out what you are going to use to power your device - Arduino or RPi? You mention both almost interchangeably. If someone has done it using a Pi then you'd be better off asking on their support site?