Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.

Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.

MarkdownPad - MarkdownPad is a full-featured Markdown editor for Windows. Features:

OneNote - Get the OneNote app for free on your tablet, phone, and computer, so you can capture your ideas and to-do lists in one place wherever you are. Or try OneNote with Office for free.

Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.

Typora - A minimal Markdown reading & writing app.