An author's addendum is a legal document that modifies the publisher's agreement and allows authors to keep rights to their work. Listed below are some free resources which can help authors negotiating contract terms with publishers:
Establishing a unique author/researcher identity is an important step to improving your research visibility and impact. There are a variety of options for creating a unique identity, with ORCID being the latest development. ORCID is well supported by many publishers.
SPARC have released this two-minute video to help authors on the topic of author rights. The video explains in simple terms the potential for wider exposure of scholarly articles when authors retain key rights.