The actual note editor should be decent.

(For instance, Letterspace!) If notes are stored as plain Markdown then the app isn't necessarily required on all platforms since generic Markdown apps are not hard to come by, but it'd still be better to have the actual app work across platforms. As I run macOS and Android primarily, this is a little tricky, since nice Mac apps usually end up only on iOS and not on Android.

I should be able to access my notes on mobile and on desktop.

Letterspace handles tags this way, but it doesn't do a whole lot else (very few configurable options, available on Apple platforms only, etc.) Ideally, tags would just appear in the notes' bodies as #hashtags since that arrangement will be the easiest to access across various platforms and apps.

I use Evernote's tags incessantly, so any replacement will need to support tagging.

(However I am willing to trust my notes to Dropbox for sync, since any files I sync through Dropbox stay accessible as normal files and will stick around locally if Dropbox dies.) Individual plain-text files with Markdown formatting would be ideal, but anything that'll keep working if the particular app goes under will be enough.

An open source application would be preferred, but I'm willing to pay for a commercial app - more importantly, my actual data must be stored in an open format.

I'm definitely not trusting my notes to another proprietary app or format.

Unfortunately there're not a whole lot of note-taking apps that'll fit the bill.

Since Evernote's recent pricing changes, I don't want to trust important personal data to their company any more, and I've been hunting for an alternative.

Index evernote replacement