https://www.allianceindependentauthors.org/

Do I use it?: I joined for a couple of years.

$119/year as an author

This organization has multiple tools for authors who are self-publishing their books. It is “a professional business membership organization that advises, campaigns for, and empowers self-publishing authors”. They offer publishing roadmaps, contracts and rights protection advice, and vetted services directory.

Although this platform has lots of good information, it wasn’t helping me to promote or sell books. Because of that limited usefulness, I didn’t feel it was worth the annual cost.