QOwnNotes
QOwnNotes – free and open source, multi-platform note-taking program with Markdown support and Nextcloud/ownCloud integration
Mark Text – free and open source, simple and elegant Markdown editor focused on speed and usability
oStorybook is a free and open source tool for writing fiction: novels, novellas, short stories, and screenplays
NoteCase Pro – free and open source, cross-platform software for organizing notes
CherryTree – free and open source software for creating hierarchical notes
Indicator Stickynotes – free and open source software for creating notes on the desktop
Simplenote – free and open-source, simple and cross-platform software for creating notes and to-do lists with the ability to sync across all your devices