WeatherPi was a e-ink weather display with basic air quality monitoring. I used it to compare when to open the windows to best fight heatwaves. It was powered by a Rasberry Pi 2B, and diligently refreshed until the display began to fail a year later.
To date, this was the fastest concept-to-implementation I've ever done, with the final product functional and on my wall in under 48 hours from thinking of it. Indeed, the decision to run in on an old pi and in an IKEA picture frame were due to using what I had on hand alone.