The core tech is tuned for performance, using local gridded files instead of a traditional database or response caching. This efficiency is what allows it to stay free.
You can try it here: https://open-meteo.com
I switched to Open Meteo a few months ago when the previous API I was using quit working. It's been rock solid and such a nice user experience compared to everything else I tried.
We've been using OWM but the One Call API quickly gets pricey when traffic spikes.
Picked up a commercial license about 3 months ago, service is amazing and have been using it for helping to provide runtime data analysis and anomaly detection for smart home thermostats.
They also provide yr.no which is widely used worldwide.
I've been using their free (2.5?) API for a while and just last week moved on to the paid-but-with-free-tier 3.0 API for more info.
You just need to put in your credit card (most likely to prove you're an actual human being) and that'll net you 1000 requests per day for free.
Then go into the settings and set a hard limit at 999 and you'll never get billed.
If whatever you're doing needs to get weather data more often than once per minute, start charging for it or cache data on your end more aggressively to not hit the limit.