The format library provides a type-safe mechanism for formatting arguments according to a printf-like format-string.
Boost.IOStreams provides a framework for defining streams, stream buffers and i/o filters.
General literal text conversions, such as an int represented a string, or vice-versa.
The Boost.Wave library is a Standards conformant, and highly configurable implementation of the mandated C99/C++ preprocessor functionality packed behind an easy to use iterator interface.
Regular expressions that can be written as strings or as expression templates, and which can refer to each other and themselves recursively with the power of context-free grammars.