pmcid
There are 4 repositories under pmcid topic.
rougier/persid
Persistent identifier library for GNU Emacs
ropensci/citecorp
Client for the Open Citations Corpus
tiadams/pmc-downloader
Batch downloads full-text PDFs (or any other soruces) from PubmedCentral OA articles
ropensci-archive/rcitoid
:warning: ARCHIVED :warning: Citation data via Wikimedia using the Citoid service