I've been working on this for over a year, and I've finally plucked up the courage to post it on HNs.
GitJournal stores your notes in standard Markdown Files. It uses standard SSH, and should be compatible with any SSH Server. I started this as while there are lots of Note Taking apps on the desktop, the mobile space was deeply lacking.
This is my attempt at building a sustainable Open Source Project - The entire code base is Open Source (no Open Core), when publishing it on the App Stores - certain features require purchasing the Pro Version. The model is similar to "Sketch" and "Working Copy" where you can purchase all the current features and new features developed in the next 12 months. I feel this aligns very well with both the creator and users, as the creator has a big incentive to listen to the users and build features that they want. (The purchase is not auto-renewing)
All the development is tracked on GitHub, so please feel free to make feature requests and vote on existing features.
I should also find an alternative to FireBase Analytics, which doesn't seem to be open source, but that isn't a blocker as I can release it in F-Droid without analytics, as the analytics were going to be disabled by default anyway.