So someone asks, "What free OSR products would you recommend for someone who has only experienced 3.X and/or 4E, but wants to branch out and learn "new" games?"
What's the answer?
My first suggestion is: sit down with the three brown books (and maybe Chainmail?) and read them all through. Pretty sure you can find pdfs via google (you could, of course, spend the time and money to hunt for actual copies). Not that I'm advocating you download hot data.
I think all told, they're like 100 pages? I can't remember.
Once you're finished, it should be apparent that OD&D is incomplete. If you're coming at this from 3x or 4e, it'll likely feel really, really incomplete. It's like a quarter of the rules you'd expect.
This is by design. Rather than deciding how throwing an oil flask and then lighting that oil works in your world for you, Gygax et al more or less leave it open for you/your DM to figure it out. This is meant to be part of the fun. It's "meant" to encourage players to think outside of their character sheet, among other things (The reason I'm suggesting your read the core rule books is because it may not be apparent what is going on in the below links without that knowledge - and because I think it's likely more effective if you just read stuff yourself rather than take my word for it).
Then go grab Philotomy's Musings over at grey-elf and skim them. I like Philotomy's because it's simple, direct and it's built through play. It's also fairly vanilla, so it's applications are broad.
And like, check out what Zak Smith has done here, to the Wizard class.
And like, this, from Jeff Rients and this.
And this, from Joey.
And lookit how Raggi does encumbrance. (art free rules linked on the right of the page)
And look at Jack Mcnamee's Dangertopia
And Jack Shear's Gothic Earth (his blog is linked below)
And Matt Finch's Old School Primer (caveat: the tone of this primer pisses some people off, I hear. I think it explains some of the appeal of OSR gaming, but it's kind of hard to capture lightning in a jar)
And go mine the below blogs for ideas about classes, settings, rules, spells, etc, etc.
And really, all of Zak's and Jeff's and Joey's stuff and these too:
Rolang's Creeping Doom
Grotesque & Dungeonesque
And over course, this.
And Jensen's Jammers
I know I've left a bunch out. Is there a "best of the OSR blogs" out there? If someone thinks I'm missing an obvious blog, let me know. I know I am, I'm just tired/lazy.
Here are a few products for money that are chosen as I feel they are indicative of what I value in the OSR:
If you're willing to shell out a little money, Vornheim is a great example of OSR-ness.
For more money than that, Blood & Treasure is a really interesting (I can't say good as I haven't finished it) adaptation of 3x for the OSR.
For even more money than that, here is part of a megadungeon.