I've been using Joplin for a few months now. So far it seems to fit my requirements better than any other note taking app I've tried - and I've tried plenty - including my own Jupyter based solution. - future proof (it's open source) - standard/open format for notes (uses mark down which is easy to write and easy enough to parse if needed in the future) - sync support and conflict detection - Kudos to their implementation here, it's very versatile. I use Syncthing and it's worked very well for me. - support for multiple clients (I use Linux, Android, OS X and Windows) - stable (no issues so far)

The major issue I have is it doesn't support stylus based notes like Onenote. A partial solution would be to extend Joplin to support additional file types so I can keep all my notes together when they are different types. For now, I keep my written notes separate.

If stylus support isn't a requirement for you, I strongly recommend Joplin. I've tried a number of closed and open source note taking tools - Joplin hits the sweet spot for me. For a long time I used Jupyter for taking notes with custom scripts for Search. It's been pretty good however it had two major shortcomings: no android client and the Jupyter client had poor conflict detection when using a a file based sync tool like Syncthing.