I recently started using Phosphor Icons and I’m impressed with how flexible and beautiful they are across different weights and screen sizes. Curious what other folks are using these days, especially in production apps.
Not really open source but still having a useful free library, I like Fontawesome a lot. If you do buy a license for the whole thing, it is yours to keep and use and doesn't expire. You only have to upgrade if you want the stuff that's added in a later release. It's a very fair, developer-friendly business model.