[madospace]

Actually most task management systems allow that today, through APIs, but you will need some glue to fix them together, like IFTTT or Zapier.

This is not limited to interoperability, cross domain / organization collaboration tool. It is almost like asking what sort of e-mail tools can be built on top of email protocol.

You are right about the commercially viable aspect. But if I wanted to make it commercially viable I would not have made it open.

I think something like this WILL be the `interoperate` set of data that you are talking about.