Can you solve this riddle for a STEEM prize?

I can't be seen, I can't be touched. I can give you anything you want, but not forever. I can make you see the impossible but you might not remember. What am I?

Source

There is a grand prize of 0.005 STEEM for the winner and three 0.001 STEEM runner up prizes.

The winner is the first correct answer. After 7 days the runners up will be randomly selected. I will use a random number generator and assign numbers to all correct answers and the three chosen will win (It's a small prize but mainly just for fun). After 7 days I post an answer/identify the correct answer and pay out the rewards.

Please remember to follow and optionally upvote if you like this post or give an answer, have fun!