The initial commit for the Java implementation of the OpenSignals for Services API has been pushed to the GitHub repository.
A concept guide is in the works and will be published later this week. In the meantime, if you are interested in learning more and maybe even making some design suggestions a good starting point would be to look at the Signal and Status enum classes within the Services class file.
There are currently 15 standard signals that can be used to describe most service-to-service interactions across various communication technologies and call invocation styles. For status, which is inferred for a particular service by way of signals emitted or received, there are 5 valid status values.