Renegade (which is the free, stripped down version of Corruption), but my God, this is full of nuggets to borrow and steal from.
It's not fancy - single column text. The amazing thing is this PDF is bookmarked and hyperlinked in part. There are RPG products out there that scream to have their PDFs bookmarked, and here we have a free PDF that went that extra step. Kudos.
What is worth stealing?
The Animal Companions section - but I'll be stealing from this to help flesh out my NPCs in my ACKS campaign - don't tell my players ;)
The adventure creation section starts out merely okay, but then hits full throttle with the Rooms, Caverns, Furnishings and Accessories table - people pay for random tables like the ones included to help them flesh out dungeons, so if you needs some table look no further. Remember, the price is right.
Tricks & Traps, Wilderness Encounters (using 3d12!), Climate & Terrain, Government Types - the list of tables and lists goes on and on. Why bother rolling? Just us it for inspiration.
Decent monster and magic sections are also included.
Really, raid Renegade for what you need in the OSR game you are currently playing. Even the classes have interesting tweaks (not that I'd run them as is, and if I wasn't going to run them as is, I'll keep the classes I have ;) that you may want to borrow pieces of.
Definitely worth a (free) look ;)