Topaz is written in Python on top of the RPython translation toolchain (the same one that powers PyPy). Its primary goals are simplicity and performance.
Because Topaz builds on RPython, and thus much of the fantastic work of the PyPy developers, it comes out of the box with a high performance garbage collector, and a state of the art JIT (just-in-time) compiler. What does this mean? Out of the box Topaz is extremely fast.
Topaz is far from complete and is missing many builtin methods and classes. However, it does have nearly every element of Ruby, including classes, blocks, many builtin types, all sorts of method calls, and much much more. We don't yet consider it stable, but it's getting closer every day.
Give a shout out to Alex Gaynor for his hard work on this.