Stirling engine! Technically, it's powered by the heat differential between your hand and the surrounding air. You could place this engine on top of an hot water of cup or cup of ice and it would still run!
/r/gifsthatkeepongiving: Gifs That Keep On Giving - This is a subreddit dedicated to those GIFs that just keep on giving. Whether they are mind expanding, funny, or just plain awesome, they are welcome here. - July 31, 2022 - 13:15