The GFS (Global Forecast System) is NOAA's global numerical model. It runs 4 times daily (00, 06, 12, 18 UTC) at ~13 km resolution, producing forecasts up to 384 hours (16 days). Its data are completely free and open.
Comparison with ECMWF
Although the European ECMWF generally outperforms GFS in accuracy, especially beyond 5 days, GFS is widely used for its free access and rapid availability. It is the base model for many free weather applications and services like Open-Meteo.