Joplin is a note-taking and to-do application with synchronization capabilities for Windows, macOS, Linux, Android and iOS.
I stumbled upon this app when looking for a good, open-source alternative on Linux for Evernote, and I have to say that Joplin absolutely delivers: open-source, markdown, live previews, multiplatform support.
With its support of OneDrive, WebDAV, Nextcloud, and Dropbox, I could easily install the app on my mobile and my laptops (both at work and at home), and always have my notes with me.
The markdown support and live preview allow me to write blog posts on the app directly, that I can then copy and paste on the write.as interface for publishing.
The ability to keep lists and to create separate notebooks is really useful: I use lists on my phone to keep track of my to-do stuff and keep lists and notes separated in notebooks.
Last, but not least, Joplin supports encryption, a good extra step to make sure that your data remain yours, especially if you use OneDrive or DropBox for storage.
I've been using Joplin for a couple of years now and, while the app could use some polishing, I always keep it installed in my devices, and make good use of it.