Other options that are open source include:
drip. https://dripapp.org/
Bluemoon https://gitlab.com/ngrob/bluemoon-android https://www.nilsgrob.ch/work/bluemoon
Periodical https://arnowelzel.de/en/projects/periodical
drip. https://dripapp.org/
Bluemoon https://gitlab.com/ngrob/bluemoon-android https://www.nilsgrob.ch/work/bluemoon
Periodical https://arnowelzel.de/en/projects/periodical
The sharing part makes that a little less common.