After Leanpub, I uploaded my book Space Apps for Android for sale on Gumroad https://gum.co/spaceappsforandroid
I chose Gumroad for two reasons. The first is Gumroad, along with Leanpub, supports selling works in-progress like Space Apps for Android, which I continuously expand and update. The other reason is I wanted to experiment with Gumroad with a real product. This will help me create and sell more ebooks, courses, and other products on Gumroad.
Bonus reason: I wouldn't mind making a few bucks.
Now I need to patiently wait for the first sales, to verify my account, and reader reviews, a requirement for enrolling in the Gumroad Discover marketplace.