QuantLib is an open-source C++ Library for quantitative analysis in Finance, and the QuantLib project was started by a few Quants in 2000. Now QuantLib project is Luigi Ballabio and ferninando Ametrano.
Secondly, QuantLib has been ported to other languages:
QuantLib.org provides a very good API Doc, but you may still want to take a look at other sources for API documents. The following is a short list of links for QuantLib API Docs.
QuantLib Java API Docs
QuantLib API Docs generated by Doxygen(v0.3.4)
C++ Design Patterns and Derivatives Pricing 2e
QuantLib on YouTube
In addition, some commercial software products are also available: QRM, FinCAD, Numerix, SunGard-FastVal, Savvysoft, Quantifi, Pricing Partners Cie, Bloomberg, Intex.