Opensource.com - https://opensource.com/article/17/12/joplin-open-source-evernote-alternative
Joplin is an open source cross-platform note-taking and to-do application. It can handle a large number of notes, organized into notebooks, and can synchronize them across multiple devices. The notes can be edited in Markdown, either from within the app or with your own text editor, and each application has an option to render Markdown with formatting, images, URLs, and more. Any number of files, such as images and PDFs, can be attached to a note, and notes can also be tagged.