Pandoc https://pandoc.org is described as a Universal Document Converter. It can convert markdown (and quite a few other formats) into ePubs, PDFs, doc files, etc. If you need to produce eBooks, Pandoc is a more powerful tool. It's been around for quite a while, and it's very well documented.

pandoc supports wide variety of conversions from one format to another, markdown to epub is one of them.

I use pandoc to generate pdf/epub from GitHub style markdown. Here's my custom script for epub: https://learnbyexample.github.io/customizing-pandoc/#customi...

Epubs are zip files, I wrote PHP code that generates the file using the specification. Use the command line apps that already exists if those do the job but if you want to control exactly how the epub content looks don't be afraid dig a bit.

Check out Pandoc!