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.
Fairmat is a derivative and capital investments modelling tool. It permits you to build a pricing model for many financial projects (or derivative contracts) using a graphical representation blended with a high level algebraic language. It is also possible to use it to evaluate projects and perform real options valuations. The platform can be extended using a plug-in system.