This consists of around 50 short eBooks (and one notebook) in the crossdressing / femdom erotica niche.
When no work is put into it, it generates between $50 and $100 per month. With some promotion on Twitter, it can be around $200. The best month was around $350 for a few hours of work including a few new books and some Twitter activity.
I can't release audiobooks directly through Amazon because I reside in a country where that's not possible. If you do, you can easily multiply the profits by creating audiobooks.