Substack is a publishing and paid subscription platform. It is most often thought of for newsletters, but it's more of a combination newsletter + blogging platform.
It is a fully hosted, proprietary, free to start platform. They charge 10% of fees you collect.
As of October 2020, you can pay $50 one-time to add a custom domain.
My personal recommendation if you're going to use Substack, is to use it with a custom domain. Then, all the links going to your content are portable should you switch platforms later.