Ben Milton's recommended reading list for old school gaming is worth a look. It's choke full of interesting articles.
I'm also digging through Low Fantasy Gaming, a free D20 old school game. It leaves the first impression of being a gentle bridge between 5e and old school Sword & Sorcery. More to come.
You might like Appendix N by Jeffro Johnson. It's an enlightening read.
APPENDIX N: A LITERARY HISTORY OF DUNGEONS & DRAGONS is a detailed and comprehensive investigation of the various works of science fiction and fantasy that game designer Gary Gygax declared to be the primary influences on his seminal role-playing game, Dungeons & Dragons. It is a deep intellectual dive into the literature of science fiction's past that will fascinate any serious role-playing gamer.
Here is a link to the Goodreads page.
James & Robyn George released Orpherian Scrolls (aff), a dark fantasy supplement for Blood of Pangea (aff).
Blood of Pangea sits right between being a narrative and an old school game. D6-based rules-lite unique system, read my review here.
Blood in the Snow is a free mini-adventure for old school games:
Farms in the hamlet of Winterton are being raided at night. Who, or what, is doing the raiding is a mystery. Animals have disappeared and now a visiting merchant has gone missing. The only clue is a blood drenched hat sitting in the snow along a stretch of road.
Don't forget to get Black Pudding #2 (aff), the old school visual zine by James V. West. Pay What You Want.