The Glatisant, an OSR Newsletter- literally just sign up for it and go, if you have a busy life this is gold.
The Feedly Save vs. TPK Blog Collection
(it's old with many defunct blogs, I recommend you use your computer
first and add whatever blogs you can find to it. Send the OPML over!)
Principles
Throne of Salt's Original, Simple, Ready to hack - I far, far like the term Open Source Roleplaying
Cue Praise Singing!
Fantasy Heartbreaker - a game made on the framework of D&D, with interesting innovations. Seen by some to be hubris, by others an excellent past-time with a sincere, deep love of the hobby.
Also the author of "Troika!" but on his blog - I love this article in its exhausted rambling beauty
OSR Discord Invite - Join the convo!
"Appendix N" - the inspirational reading appendix in the AD&D 1e PHB,
Information, Choice, Impact by Chris McDowall - Good OSR Referee advice
On Edge by Ajey Pandey - A Good Twitter thread on conceptualizing edginess.
Advanced Quickstart or, Just hack it:
Scarlet Heroes Quickstart
(drop the weird damage rules, play as per normal, drop the fray dice,
trait=race [allowing you to make up races and just justify a roll with
"the descriptions says so."] hack as you please)
Into the Odd (check the sidebar of the blog)
An Into the Odd Syllabus - A Google Doc with a TON of hacks
Vyf Munte (My Own RulesTM which will be posted in due time)
Weird Old-School cliques/movements/parts/factions
Each identifiable, but the borders are blurry to non-existent. Consider them odd outpouchings to the main agora of the OSR
Artpunk - I love this with all my heart. Some people think graphic design is a useless addition if the writing is even slightly bad. We spend most of our brainpower processing sight so checkmate.
A love/devotion to White Box or B/X - I don't mind it, oftentimes they have interesting takes on the odd mechanics of those earlier editions which are worth reading, these are the half-fondly named 'grognards' of our community. Great pity that a large proportion of them are rather toxic and/or troll-y.
Arnesonian/Ancient/Pre-School Roleplaying - A weird off-branching of the last couple years concentrating on Dave Arneson's contribution to the hobby alone; stating (with evidence) that he started roleplaying all by himself, which Gygax then just hacked into his Chainmail rules. Tries to recreate those types of games. Hyper-simple gaming. See The Landshut Rules and Sword & Backpack.
Old-School Storygame Roleplaying - Blurs with Arnesonian Gaming. Sort of really took off after Dungeon World (I think? The Burning Wheel came before). OSR games are already weirdly blurry, these just focus on the story element. Interesting, not my preferred style. A good example would be The Burning Wheel, Dungeon World, World of Dungeons or Trophy Gold.
OSR of other RPGs - Advanced Fighting Fantasy has Troika!. Warhammer Fantasy Roleplaying has Zweihander.
The GLoG - Stands for the Goblin Laws of Gaming. Arnold K. of Goblin Punch released a series of home rules for his own roleplaying game. Cue enthusiastic hacking by many - Many different hacks, Many Spells, Many Classes. Seriously Madcap & DIY. I like the spell system a lot.