Mastodon app got a "non-free net" anti-feature tag because it talks to joinmastodon.org... Oh and also because it uses FCM, the Google push notification service. Only on devices that have Google services, so, like, there aren't any privacy implications for that really. But without the closed-source Google library, because that would've also meant "non-free dependencies". F-Droid maintainers were very confused when they found out that I reverse engineered the Google library and made a first-ever 100% open-source FCM-enabled app.