My favorite one was called Statusboard. It was an iOS app from Panic (yes, THAT Panic) which turned a spare iPad into an ambient data display.
Configuration was easy, and on mine I showed RSS feeds, mail information, weather and more.
I used it on an old outdated iPad I had laying around. Other people I knew did the same, but hooked it up with the lightning → HDMI wire to 40-inch flat screens they had left over when everyone upgraded to 4K.
Sadly, Panic EOLed it years ago. Which is a shame because that happened right about the time that surplus iPads and cheap flat-screen TVs became a thing.
Now, with so much legacy display tech headed to landfills, I wish some iOS developer would make a similar app and make a dent in the flow of e-waste.