I built Premium Ghost Theme marketplace http://www.gtheme.io/ to sell premium ghost themes. I designed most of the themes because I have chicken and egg problem. Now I get about $100-$300/m revenue.
Most people still dont know what is Ghost https://ghost.org/ yet. It is CMS that like Wordpress, but built on NodeJS.
My passive income, Ghost Theme marketplace http://www.gtheme.io/ Revenue around 100 USD per month. Running for half year need more marketing for better revenue. Ghost blog is the next big thing in blogging space.
Ghost (https://ghost.org/) will be the next big blogging platform and GTheme.io is the first Ghost Theme marketplace that focus on Ghost only. Ghost App marketplace is ready and waiting official Ghost App available.