SeaPig

SeaPig is a straightforward and efficient piece of software that helps you quickly convert text to HTML using the widely-accessible Markdown language.
You can get started with the application with the minimum amount of effort since it does not require installation or any type of configuration on your part. To deploy the app, simply unzip its package and launch it via the designated executable file.

User-friendly Markdown editor

Once started, you are greeted by the application's somewhat outdated yet highly functional user interface. As is the case with most Markdown editors out there, SeaPig also features a fairly simplistic layout, which should help you get to grips with the app's basic functions in practically no time.
This said, you will notice the useful top toolbar that makes it straightforward for you to choose the key bindings from the drop down menu, to open new or already existing markdown files and to save your current work. Furthermore, from the same toolbar, you can also hide the left-sided text editor or the right-sided preview pane.

It may not bundle a live preview feature, but other than that it has almost all bases covered

This is a good time to point out that unlike other, more modern Markdown editors, SeaPig does not feature a real-time preview pane. To view the changes, you will have to manually refresh the HTML preview instead (easily accomplished with the help of the dedicated button located on the toolbar).
Besides all that has been said, you should also know that the utility can easily export your projects directly as HTML files and PDFs. Also noteworthy is the fact that SeaPig can be run just as efficiently on all major operating systems out there, namely Windows, macOS and Linux.

Overall, a decent cross-platform Markdown editor

Taking everything into consideration, despite its outdated and simplistic looks and the fact that it does not bundle a live-preview pane, overall, SeaPig can still be considered an efficient Markdown editor that can surely help you convert text to HTML.