Cool - a complete Lisp that runs directly on the RCX. Perfect for the holiday season.
Unfortunately no OS X version, only something for Windows or Linux - and the latter only for the serial tower. Let me see if I can get something working for OS X with the USB tower. I also stumbled upon TinySOAR, a complete AI Agent Runtime for the Mindstorms RCX brick. Also very interesting - and hopefully also runnable on OS X through its embedding in TCL. And also new to me is the Java VM for the RCX: LeJOS. I don't like Java much, but it's definitely interesting for the RCX. And the oldy-but-goldy: LegOS, the complete operating system for the RCX written in C. However, due to its rather hefty toolchain (a complete GCC configured as a cross-compiler), it's somewhat tricky to install. Besides, it's now called BrickOS and is incidentally also under the Lisp as runtime. Here's the original article.