Bus Scheme is a Scheme written in Ruby, but implemented on the bus! Every programmer must implement Scheme as a rite of passage; this is mine. Note that all the implementation of Bus Scheme must be written while on a bus. Documentation, tests, and administrivia may be accomplished elsewhere, but all actual implementation code is strictly bus-driven. Patches are welcome as long as they were written while riding a bus. (If your daily commute does not involve a bus but you want to submit a patch, we may be able to work something out regarding code written on trains, ferries, or perhaps even carpool lanes.) Bus Scheme is primarily a toy; using it for anything serious is (right now) ill-advised.
Bus Scheme aims for general Scheme usefulness optimized for learning and fun. It's not targeting R5RS or anything like that.
I haven't actually used a real Scheme yet. Everything I know about it I've gathered from reading The Little Schemer, watching the Structure and Interpretation of Computer Programs videos, and reading lots about Common Lisp and Emacs Lisp. If there are huge gaping flaws in the implementation, this is likely to be why.