Ultra Agent sets released in 2015 feature an interesting type of brick, which is called AppBrick (LEGO marketing name) or Brick, Modified 1 x 1 with Stud on Side and Conductive Element on Opposite Side (AppBrick) on Bricklink:
This is how LEGO describes it in the AntiMatter's Portal Hideout (70172) set:
Build your AppBrick Gadget included in this set and play out cool missions on your tablet
Basically you build a small model with a few elements and put it on the screen (of the phone/tablet) to interact with a dedicated app as shown in the instructions:
This brick is made of some new material, which is of conductive plastic and it works with capacitive touchscreens. That is, you can control whatever you wish on your phone/tablet screen using this brick with your hands without your fingers actually touching the screen. This is a pretty cool feature. However, even though this element has a useful stud with a hole on the backside, usage of this element is rather limited. I wonder if more LEGO elements exist featuring the same properties?