There's inkdrop. The iOS app is pretty limited but it syncs with the desktop app and has an electron (I know, I know) app for Mac, Windows, and Linux. It's exte

There's inkdrop. The iOS app is pretty limited but it syncs with the desktop app and has an electron (I know, I know) app for Mac, Windows, and Linux. It's extendable with plugins. I've been using it for a couple of months and I love it.