Simplenote is a note-taking application with Markdown support. In addition to being accessible via most web browsers, cross-platform apps are available on Android, Linux, Windows, iOS, and macOS. Simplenote has an externally accessible API, allowing other clients to be written: macOS Dashboard widget DashNote; nvPY, a cross-platform Simplenote client; amongst others.

NOTE: This is only to provide appimages, I am not the developer.