The idea is to take a standard office laptop (like a Thinkpad) and mod it with a graphics tablet (similar to the ones by wacom). The tablet would be mounted behind the LCD of the laptop, so you can draw directly on your screen. Maybe it's a cool idea to wire the USB connection of the tablet to one of the outgoing USB ports so you can use your (unpowered) Laptop as a graphic tablet for another PC (with a USB-A to USB-A cable).
In a second (optional) step, to make the whole thing more useable, the LCD and the tablet could be mounted into a 3D printed, turnable laptop cap so you can close the laptop and have the screen on the outside like a tablet.
A third (optional) step would be to install a capacitive foil on the LCD to turn it into a touchscreen.