Joplin

For anyone who has been stranded by an app once and refuses to let it happen again. Joplin is open source, runs on Windows, macOS, Linux, Android and iOS, and lets you write in Markdown or a rich text editor. You pick where your notes sync, Joplin Cloud, Dropbox or OneDrive among the options, with end-to-end encryption on top. It looks plainer than the commercial apps and takes a few more minutes to set up. In return, no company decides what happens to your notes, and the Markdown underneath stays readable long after you have moved on.