Probably the most important set of libraries other then the STL, Boost offers a huge amount of functionality. Libraries featured in Boost may eventually be included in future C++ standards.
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Xerces is a validating XML parser with support for Dom, SAX, XML Namespaces and XML Schemas. This library is provided by the Apache foundation.
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Another library from the Apache foundation, Xalan is an XSLT processor, compatible with Xerces.
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wxWidgets is a lightweight cross platform GUI framework. Unlike some widget kits it uses the native widgets of the current platform. This gives it a more native feel and makes it fast.
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