Most notes apps are websites with an app wrapped around them. They open to a spinner, refuse to load an old note in a tunnel, and lose a paragraph when the connection returns mid-save. That is a strange property for the place you keep your thinking.
Dash is offline in the plain sense: the notes are files on your device and the app never needs a server to read or write one. Sync exists, but as something you switch on, not as the thing holding the app together.