The Rules Cyclopedia is my second favorite RPG that we never ever get to use (well, we use the occasional rule from it) because it’s too close but yet so far to our normal, slightly more 5e-tilted edition mashup. During the OGL scare, the RC was one of the games I considered (not that it’s open source either, but OSE and DD are and they’re reasonably compatible).

I was reading some OSR fanzines with a ton of custom classes and monsters today and they’d probably be usable with RC too, with maybe just the XP curve changing.

I have the kinda blurry (but works just fine) PoD reprint of the US original. This Japanese edition is especially beautiful.