Unity3D Asset Store
I have been a Unity Asset Store publisher since 2012.
I have had two packages reach the front page of the store, which generated a good amount of income, but that was in the early days where I had a lot of free time.
As my education started to take more of my time, I decided to cut down the amount of time I use on the asset store. Now I mainly answer emails and make sure that my packages work on the newest version of unity.
I still earn some money from the store each month, but it is not my main source of income anymore.