Trent and Ophelia both knew how to turn on and off the touch lamp we used to have on the headboard when they were kittens. It was so cute to watch them go up and touch the top of the lamp with their nose.
They would usually do it either when I was in bed reading and they wanted me to get comfortable to go to sleep, or at about 3:00 in the morning when they wanted us to get up and play with them or pet them.
I knew one cat who could unlock and open his people's front door. We came home one day and FREAKED out because the front door was standing wide open and she knew she had locked the door! We thought it had been broken into, but Dice just wanted to go outside.
Needless to say, the furniture was rearranged so Dice couldn't reach the front door anymore.