The standard app is free syncing across Linux, Mac, Windows, iOS, Android and the Web. It is AES-256 encryption enabled for privacy and if you lose your password, you lose the data (no workarounds or backdoors). It can also import for offline archives (so you can import from other services like Evernote after doing an export), or you can archive your data out of the service.
The editor is very plain and simple but gets the job done. There is an optional paid service for theming and additional editing features through extensions that can be enabled.
See https://standardnotes.org/ 
Standard Notes | A Simple And Private Notes App
Standard Notes is a private notes app that features unmatched simplicity, end-to-end encryption, powerful extensions, and open-source applications.