From the project’s website: “Emacs-IDE is an Integrated Development Environment (IDE) interface for Emacs (code browsing, compilation, debug…).”
How is this related to ECB (EmacsCodeBrowser)?
I don’t think they are related. Maybe Emacs-IDE uses ECB, I don’t know. However, the former is designed to be run in a stand-alone Emacs instance, not as a package like the latter is.