ProcPile is a pure Ruby distributed computing cluster environment. Its goal is to allow fast prototyping on smaller datasets, especially those where serialization and deserialization are minor expenses relative to the core processing task. Once the algorithms are settled, you should be able to scale out to full production usage. At that point, you can replace the core processes with Ruby modules written in C (or Inline::C), or move the design to a more "grown-up" clustering environment.
QuantLib is a cross-platform, quantitative finance C++ library for modeling, pricing, trading, and risk management in real-life. It is also wrapped as Python/Ruby/Scheme modules. Extensions for Excel, R, and Mathematica are available. Other such extensions are under consideration. QuantLib offers tools that are useful both for practical implementation and for advanced modeling. It features market conventions, yield curve models, solvers, PDEs, Monte Carlo (low-discrepancy included), exotic options, VAR, and so on.