I discovered it recently, and it seemed quite easy to make, so I decided to try...
I'm doing everything from scratch, mixing the oat with water, sugar, and raisins, for a few days. That's going to be the starter.
I also ferment honey with garlic and various spices. (Long process)
Another one that I make is fermented ginger (grated). I will add it to lemonades, or use it as starter, to ferment pineapple juice.