yeah! I just started one a few weeks ago

I poured off some whey from raw milk kefir that had been in the fridge for months (keeping the grains alive, we're dairy-free otherwise), and used a mix of tapioca, brown rice flour and millet flour. The first few times I fed it, I threw out half first, to dilute the whey, and just added water and flour mix. It lives in a mason jar on the counter now.
I've been using it to make gf bread and pancakes, my first real venture into gf baking after a year off most grains. So far, so good. Even dh says it's a great sub for the homemade gluten bread I used to make.