Each separate child project is still an OTP application, even if you do not use "OTP" features in them. OTP app is just the term for that artifact, similar to a

Each separate child project is still an OTP application, even if you do not use "OTP" features in them. OTP app is just the term for that artifact, similar to assembly or archive in other languages but it is not only terminology, each one will have `start` called when the VM starts, even if they don't spawn any servers.