I made a little OSR game based on Ruins & Ronin/OD&D: Shinobi & Samurai. It features nine classes, simple and flexible rules bases on OD&D/R&R, many Oriental weapons and even more monsters (about 150). It's short (less than 100 pages) and all classes, spells, items and rules take less than 30 pages.
I kept it simple: There are no ability scores, no alignment or XP charts, time and distances are kept abstract, spell lists are streamlined with room for interpretation and monster fluff/crunch are kept separate. But don't worry, the system is still compatible with the other OSR systems and everything can easily be re-added.
I wrote a companions with nonhuman races, optional rules, an honour system, spell points and a skill system as well, but I want to keep that separate from the core rules for now. Shinobi & Samurai is free and you can download the PDFs here.
It's not 100% polished yet, but I wanted to get a a version out instead of fiddling with it for month (plus it's free).
Regarding XP: XP and me is a mixed relationship. In OD&D it wasn't too relevant (except when you use the thief). In AD&D it was arbitrary. Here, I tried to balance all classes so they could use a unified XP chart. However, I haven't done extensive playtesting, so I can't make promises here.
One house rule (at will become a rule in v1.2): The samurai starts with a katana.
Yup, I wanted to try out what happens if I don't have the spell description make up 80% of the rules. That's not true for OD&D and not generally a bad thing, but I kind of like knowing all spells and their effect by heart. Plus, I unintentionally never used precise spell range anyway.
Credit for the Bakekujira partly goes to Ned Martell and his Oriental Monsters BD&D supplement.
I just figured I'd make a list of the 20 or so retroclones... which then became about 50 and now over 100. Even the number of "core" (mechanical, not spiritual) clones is impressive with some true gems hidden here and there.