Disclaimer: I am the author of Helpinator - a single-source technical writing tool. It is for Windows, but some of my customers successfully use it on Mac via Parallels. It has EPUB/MOBI/PDF support.

I recently added LeanPub support too, so now you can publish the same project on LeanPub too. Here's the blog post about it: https://www.helpinator.com/blog/2019/08/23/leanpub-tutorial-...

There's also a post by Davide Barranca depicting his experience on getting LeanPub book published paperback with LuLu: https://www.davidebarranca.com/2019/04/printing-leanpub-book...