Common Works Registration (CWR) is a protocol and data format for registration of musical works, used worldwide. Matija Kolarić is the leading author and consultant in the field.
CWR Tools is a set of several free online tools, based on open-source music catalogue software DMP (Django-Music-Publisher), and Music Metadata Python libraries.
If you need basic battle-tested CWR-capable music catalogue management solution, use DMP. If you need more features, with professional support, That Green Thing is the obvious choice.
This is a long series about CWR, with many practical examples made with CWR Tools.