There is a perception that DOIs signify something being 'official', whatever that means. But in the publishing ecosystem (e.g. Crossref), it's whatever the publisher decides to publish. There's a wide range of publishers who publish anything from books to peer-reviewed works to preprints.

Two examples of DataCite members are OSF.io and Figshare.com . They have very different models. Figshare lets you share and assign DOIs to arbitrary research files. OSF lets you version-control your research and assign a DOI to the project.