Found these examples by quickly googling:
https://www.trueenergy.io/app/
https://play.google.com/store/apps/details?id=com.sense.andr...
https://play.google.com/store/apps/details?id=com.tibber.and...
EDIT: to answer the question: yes, these apps use something called "Nord Pool" which publishes hourly electricity prices (in Swedish): https://elavtal24.com/blogg/tibber-greenely/
https://fsr.eui.eu/time-of-use-and-dynamic-pricing-rates-in-...
All the usual communist elements (Jimmy Carter, California) have been slowly making progress on introducing it since the 1970s, but mysteriously a lot of lies sprung up about how it would harm the poor. And the USA is really caring about the poor not using as much fossil fuels as they possibly can so it got kind of squashed.
It’s _not_ like that in the states? In Denmark people are sharing spreadsheet that can tell you when to run the washing machine to save on electricity since the energy crisis following Russias invasion of Ukraine has pushed prices enough that these optimizations become valuable to regular consumers.