I have. I'm on the team that's been developing it for the past four years. It's nice to see graph databases getting some popular traction at last. (I was into them before they were cool, of course.) I've only just started looking at Cayley but it looks like there are some significant differences between the projects. Orly is designed for high-speed, high-volume applications that need large-scale storage and consistent transactions. We're more OLTP than OLAP, which seems to be the way Cayley leans. Most graph systems tend toward analytic applications.