“The DOI (Digital Object Identifier) is an international standard (ISO 26324) managed by the International DOI Foundation, which provides a system to support persistent identification of content objects and related entities in digital networks.”

“You do not have to be a member of the DOI Foundation in order to assign DOI names but you do need to be affiliated with a Registration Agency in some way. DOIs are, and will always be, free to resolve. A DOI can apply to any form of intellectual property expressed in any digital environment. An entity can be identified at any arbitrary level of granularity. This means that, for instance, DOIs can identify a journal, an individual issue of a journal, an individual article in the journal, or a single table in that article”

• https://doi.org
• https://www.crossref.org/services/content-registration/
• https://www.doi.org/the-community/existing-registration-agencies/
• https://www.doi.org/the-identifier/resources/
• doi:10.1000/292
• etc

see crossref

• US based
• pricing https://www.crossref.org/fees/

see datacite

• based in Germany as e.v
• pricing Membership Fee of 2000€ and Service Fee of 500€ per year plus 0,80€ per DOI
• etc+

• mEDRA (multilingual European Registration Agency)
• a brand of ediSer, the service company of the Italian Publishers Association
• pricing (https://www.medra.org/en/terms.htm][details)
  • 150€ startup fee, 180–6000€ per year for 30–8000 DOIs (then 4.50 to 0.45 each)
  • additional 250€ for crossref integration (NB this is more expensive than crossref)
• guide https://www.medra.org/en/guide.htm

• not a registration agency but a Rotterdam Stichting that provides sponsored crossref membership in DOI blocks
• supports the dissemination of research content in the arts, architecture, built environment, and design domains.
• pricing from €19/yr for 5 DOIs to €99/yr for 50 (includes crossref membership).
• platforms are hosted in a climate neutral data centre by greenminihost at evoswitch -largest provider of Mac mini hosting in Europe
• CC-BY-4.0 licence for hosted content (but DOI users can also host content elsewhere)
• https://openaccess.ac/index.php/what-we-do/dois

• ONIX for DOI Metadata Schema v2.0

• https://datacite.org/blog/cool-dois/