I am now using http://pirateweather.net/ it's not quite as good as DarkSky (They use less models for prediction) but they follow the DarkSky API design so if you invested in the DarkSky API it's easy to swap over. I just use it to display weather on a few devices around the house so nothing commercial, if you are just looking for a straight replacement for DarkSky's app they have http://merrysky.net/

I'm pretty sure DarkSky's API is now called WeatherKit https://developer.apple.com/weatherkit/. A quick googling tells me you can use it with Android apps as well

AerisWeather is another option https://www.aerisweather.com/develop/api/. Disclaimer, I just started working with these weather nerds. It's a great place though, with a product and company run by developers. I recommend if you are looking for lots of neat features or need accuracy.

for my specific use-case with my Arduino/K8s setup, I found a mix of OpenWeatherMap and the National Weather Service's API to be optimal. OpenWeatherMap for broader metrics and the NWS for hyperlocal data, especially when it came to certain severe weather alerts. But tomorrow.io looks pretty interesting, definitely worth a poc