I'd second Joplin. They have lots of good sync options, including their own (pretty cheap) service. I just use the android app to read notes, but I agree it's pretty clunky to take notes on android.
I'm not sure popular is the biggest goal right now. It would definitely be nice for federated platforms to gain a bigger user base, but while the tools are growing, it's really inspiring just to think that people are willing to invest the (low or no profit) time and energy into making the internet a nicer place.
1000, in the same way pi is 3.