Please note: I get commissions for purchases made through (aff) links in this post.
Wired Neon Cities - Minimalist Cyberpunk Roleplaying (aff) is PWYW. What is says on the tin. Scott Malthouse manages to put the complete game on 2 pages. This succinct ruleset wants to be played!
Inside every old-school game is a diceless system waiting to get out, and so we're proud to announce the release of our digital version of Diceless Dungeons! Because diceless gaming is just about as old-school as you're gonna get. After all, decision-making, exploration, and role-playing are the foundations of old-school adventure, and anyone who's spent an entire session debating how best to proceed knows what we mean...
(I haven't had the chance to take a look at this game, so this is not an endorsement. But I liked BoP.)
Also, Tunnels & Trolls Fifth Edition (aff) is available as a PDF now. It costs USD $6.95.
Wayne Rossi has some thoughts on why this is an interesting game.
Print Versions of Sharp Swords & Sinister Spells are PWYW. I like this game, here is my review at DTRPG (aff).
Old School Adventures
Monkey Business (aff) is PWYW.
Something steers deep in the jungle. Rumors of a strange drug start making the rounds ... and then things start getting really hairy. Even the cannibals are upset. Monkey Business is best described as a procedural jungle crawl, all pulp and weird and very arcade. [...]
There is a shit ton of stuff. 100+ pages of background ideas, tools, generators, etc.
Jens D., the author, is a thoughtful writer at The Disoriented Ranger. I took a small peek into the PDF and I like what I saw. You want this.
Phil Nicholls has collected a list of 40 Top Sites for Storytelling GMs.
And if you're more old school, you might find Alex Schroeder's article about Rulings worth a read.
Don't forget to check out the Dungeon World Newsletter.
This is Anthony Lewis' page with lots of free supplements for various games. Nice! RPG Stuff-o-Rama.