Abricotine (FREE, open source)
Abricotine supports very good instant preview like Typora, but is open source - free forever.
The editor is unmaintained as of Jul 19, 2023. The author suggests using other editors. See brrd/abricotine#347.
Atom (FREE, open source)
The editor is archived and unmaintained as of Dec 15, 2022. See https://github.blog/2022-06-08-sunsetting-atom/.