A series is a data structure much like a sequence, with similar kinds of operations. The difference is that in many situations, operations on series may be composed functionally and yet execute iteratively, without the need to construct intermediate series values explicitly. In this manner, series provide both the clarity of a functional programming style and the efficiency of an iterative programming style. Series is the culmination of many years of design and use of this approach, during which some 100,000 lines of application code have been written (by about half a dozen people over the course of seven years) using the series facility in nearly all iteration situations. This includes one large system (KBEmacs) of over 40,000 lines of code. In a nutshell: Think "Efficient MAPCAR". SERIES translates functional-style expressions into efficient loops.
RScheme is an object-oriented, extended Scheme implementation with a compiler that targets C or (RScheme's own) bytecodes. It has features expected from a modern language: an object system, reflection, modules, namespaces, safe macros, threads, a system call interface (including sockets), separate compilation, and persistence, as well as the formal basis and power of the Scheme programming language. RScheme also features a powerful, elegant foreign code interface.