Imagine that technology has progressed to this point:
Device shape is irrelevent, but imagine a sphere about 4" in diameter.
using levitation it hovers around your head, like Tatl the fairy from Zelda: Majoras mask
It contains an A.I. smart enough that you can talk to it like a real being and it would be able to respond as such.
Optionally it could be linked to your brain, so you can give it commands telepathically
it has holographic capabilities, so it can project anything that you wish. Such as computer monitors for data display
it has a essentially infinite connection to all data repositories, with a highly efficient search algorithm. Allowing it to access any information you ask for (providing you have permission, of course)
it can allow for instantaneous communication with any person no matter how far away, whether verbal, visual, or textual. It also does automatic translation to any language, even sign languages.
it has either Star trek like holograms (that provide tactile response) or tractor beams, which allows it to manipulate or operate any object.
using the star trek holograms and levitation, it can create objects such as flying cars that operate just like the real thing.