I'm sure I'll forget a few people who have released free publications I use (or would use,) but I'll draw attention to a couple:
- Daniel R. Collins, for his Target 20 system; it's simple and allows me to keep close to the original rules while simultaneously moving closer to a system that doesn't require the books during play.
- Dyson Logos, for his geomorphs. Many other people have created geomorphs, but Dyson set a new standard, plus he's actually bundling his into PDFs, making it easy to go back and "catch up".
- Kellri, for the Old School Reference PDFs. Sure, they're technically for AD&D, but they're extremely useful.
- Bloggers in general, because blogging is technically publishing, even if the blogger doesn't gather material into PDFs or go hard copy. How else am I going to thank Trollsmyth for the "Shields Shall Be Splintered!" rule? And even though David Bowman creates PDF material, it's the (re)stocking table embedded in one of his old blog posts that I use more than anything else.