GPP - GPP is a general-purpose preprocessor with customizable syntax, suitable for a wide range of...
GNU M4 - GNU M4 is an implementation of the m4 macro preprocessor.
GCC C Preprocessor (cpp) - Top (The C Preprocessor)
PP - A generic Preprocessor - P is a text preprocessor designed for Pandoc (and more generally Markdown and reStructuredText).
Gema - General purpose text macro processor.
TXR - Pragmatic, convenient data munging language.