BDDs [bry86] (or more precisely ROBDDs) are efficient data structures for representing a boolean formula. They are widely used in formal verification, in particular symbolic model-checking. Ruby- BDD, based on Buddy, provides access to BDDs from Ruby, a powerful and very easy to use object-oriented language. The purposes are quick prototyping and education.
Sanzang is a compact and simple cross-platform machine translation system. It is especially useful for translating from the CJK languages (Chinese, Japanese, and Korean), and it is very suitable for working with ancient and otherwise difficult texts. Unlike most other machine translation systems, Sanzang is small and approachable. Any user can develop his or her own translation rules, and these rules are simply stored in a text file and applied at runtime.
omnisode generates a Ruby program to use long Taylor series to solve systems of ordinary differential equations. It generates code to solve the equations in either Maple or Maxima. Using the Taylor series, estimates are made of the location and order of poles. It has been greatly re-worked the last few years, and tested quite a bit recently. Support may be extended to other languages in the future.