Hi!
In any operating system, I use mostly Typora for notes so I can sync the notes via Google Drive. I use Google Tasks and Google Kep.
In Linux, I use Indicator Sticky Notes and Xpad for small notes over desktop, so I do not forget of doing what I must. I also tried Joplin, but it is unstable via Arch Linux due to the fault of NodeJS.
In macOS, I use mostly Numi of which I am a contributor of translations and Typora.
In Android, as it does not have Typora, I use Monospace, Scrittor and Writer.
I find interesting HackMD indicated Sandeep Panda and Bootsnote indicated by Ryosuke. I will try them.
I dislike Evernote, because downloading them offline is not free and it does not have a version for Linux. The formatting is limited.
I loved OneNote, because formatting is not limited, but it is not responsive in the mobile phones.