Years ago I did what every GM does: I wrote my own RPG to reflect my play-style. It had many names during development, but due to the (non-)availability of domain names, it was eventually officially named Dekahedron. The intent was to create a rules-light, skill based system that was unencumbered by copyright or licensing hassles.
Time marches on, and preferences change. For reasons that I'll probably put in a future post, I've moved away from skill-based systems and my current preference is for attribute-based systems. Coincidentally or not, this is very much in-line with what I believe to be the essence of the current "old school role-playing" movement. This led me to work on a new version of Dekahedron. This isn't the Dekahedron 2.0 that I talked about a few months ago, rather this is a new project. I'm currently calling it Dekahedron: Old School Revision, or "Old School Dekahedron" for short. When I'm feeling particularly terse, I just call it "OSD".
The core rules — saving throws, task resolution, melee combat — are all pretty straight forward, and already written. The complicated part is a magic system.
I'd decided to go definitively non-old-school for my magic system. It seems to me that all the old games centered around a list of spells. When the new style of rules-light games hit the market, the rules were so loose to give the spell casters increased flexibility, but adjudicating these became completely arbitrary. I've decided to take a page from BESM and Hero, and let players create their own spells, but with a strong rules framework about what they can create.
I'll let you know how it turns out.