We don't know any good FanCircles open-source alternatives yet.
You are more than welcome to suggest any alternatives that you know of, or ask the community for suggestions.
Alternatively, we recommend checking out LibHunt for open-source libraries and alternatives to FanCircles.
Fancircles platforms give brands their own social media platform where they own the data and relationship with the user directly. This give 100% and no and costs. D2C social media at its best