[dwaite]

There are systems designed to be federated, like email, mastodon, matrix and SMS/RCS.

Signal, WhatsApp, Slack, and iMessage are examples of services which were designed to be run by one company as part of their product. They _might_ have certain SDKs to extend that service (like bots for slack, or app extensions in iMessage) - but generally they aren't excited to shoulder the additional cost and support headaches of third parties using their infrastructure or arbitrarily interacting with the official software clients.

I don't know exactly what you mean by "ecosystem" - I'd argue the first set form ecosystems, while the second set form products.