What are premium apps / apps with a star?

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Some application APIs are more complex and require more resources from us to build integrations towards - this means that the workflows for these apps require more effort from us to deliver and support, and as a result we require the user to be on the Connect Unlimited plan in order to use them. You can only use a workflow that connects to a premium app if you are on the Connect Unlimited plan.

See which premium apps that are currently available here http://connectmyapps.com/Integrations