Hey there,
Glad you like the language :)
Fancy currently only runs on Rubinius since it compiles down to its bytecode format and relies on some parts that are specific to Rubinius at the moment.
Porting it to other virtual machines shouldn't be too hard though. I've roughly separated the standard library into Rubinius specific and non-specific parts.
As of now porting it to any other Ruby implementation isn't planned.
MRI 1.8.7 probably isn't a good target (due to how its implemented), Ruby 1.9 might make more sense since it's an actual bytecode VM.
But both 1.8 and 1.9 both lack a JIT (Just-in-time) compiler, which Rubinius offers. Also they don't support real concurrency (without a global interpreter lock) and many other things.
Rubinius is probably the best Ruby implementation (in terms of implementation semantics, features and culture) to what I'd want Fancy to run on.
I'd suggest you'd give Rubinius a try (not just for Fancy). :)
In terms of performance Rubinius might work just as well or even better for your code.
So yeah, the basic answer is it's not impossible to port, but I don't really have anything like that planned for myself right now.
And since the language is still changing somewhat (it's in pre 1.0 status) porting it to another platform at this point probably isn't the best idea.
I'm not going to stop anyone from doing that, of course, and am glad with helping anyone trying to do that.
What exactly did you want to use it for at work, if I may ask?
Cheers,
Christopher.