I’m a huge fan of the Ulysses app (Mac). If you’re a Mac user, and you’re looking for a fast and simple way to publish your ebooks on iBooks, check out this tutorial, Self-Publishing for Absolute Beginners.
It sounds brilliantly simple, and I may try it one day. Currently, I’m Amazon exclusive. I’m slapping everything into KDP Select, because of Kindle Unlimited’s pages read.