There are a few others certainly.
For the masses, we’re going to need more providers who are ethically working toward IndieWeb as a Service (IaaS). Companies willing to allow people to be the customer rather than exploiting them as the product.
Of course, if you’re running WithKnown, you’re already there with all the trimmings. If you’re on WordPress or Drupal with your own domain, you’re already there too, but you can add lots of additional interactive functionality with a few plugins. There are dozens of available platforms that will do the job and each one has a multitude of options and configurations.
All that choice comes with a spectacular amount of complexity. Hopefully some clever companies will narrow down some popular options and make them available to large numbers of people for a reasonable price.
(Personally I wonder what things might look like if your online social IndieWeb infrastructure was run by your local public library or your local newspaper?)
The community has and continues to do a lot of incredibly difficult work to make dramatically different websites be able to interoperate and communicate with one another. Many of the roads are well worn now, we need others to come and pave them to be as equitable and easy-to-use for the rest of humankind.
All this said, of course we still also have additional complex problems like privacy, safety, anti-bullying, etc. to conquer so that we don’t end up with a decentralized version of Facebook and continue repeating the same problems of the past.
Many of us are content with small, organic growth. Massive overnight growth is often a myth, and if it does happen, you can have unmanageable and unanticipated problems seen in situations like the “eternal September“.
“Never doubt that a small group of thoughtful, committed, citizens can change the world. Indeed, it is the only thing that ever has.”