User interface solutions Are there "user intefrace" solutions for Arduino based gadgets? Solutions, that is, accepted as something more or less standard by the community. I am unaware of the relevant keywords, if there are some, so let me explain:

A modern computer has a standard keyboard and a standard mouse, which together cover 99.99% of all the imaginable needs. Of course, you can plug the Arduino gadget into a computer via USB and enjoy full control via the Firmata protocol, for instance. What are the more lightweight solutions, if a laptop is too heavy, yet a pair of buttons not smart enough? In the range of smartphone to something calculator-like?

Sorry for being vague; it's a newbie question.
I doubt there are any standards for this. The reason is that 'hardware' solutions are very much more flexible than PC solutions (which by default have a keyboard, mouse and monitor) and not much more.

Hardware solutions on the other hand can have any kind of different displayed, touch screen, sensors of all kinds, leds/lights, hardware/mc controlled motors, relays, communication means etc. 

The only user interface solutions are probably the libraries which can be used for some hardware, e.g. display driver drivers, led drivers, sensor libraries etc.

Especially to combine multiple hardware items (like on a PC the mouse, keyboard and monitor) gives a user interface 'experience'. Since hardware solutions have many more different hardware options, there is not a clear 'solution' for combining so many different hardware.