C Preprocessors

cnd - A preprocessor that gives C multi-dimensional arrays.

https://github.com/inducer/cnd  

filepp - the generic file preprocessor

http://www-users.york.ac.uk/~dm26/filepp/ 

gpp -  a general-purpose preprocessor with customizable syntax, suitable for a wide range of preprocessing tasks

https://logological.org/gpp

mcpp - A portable C preprocessor

http://mcpp.sourceforge.net/ 

preprocess - a portable multi-language file preprocessor

https://github.com/trentm/preprocess 

ucpp -  A C preprocessor designed to be embeddable, quick, light and fully compliant with C99

https://code.google.com/archive/p/ucpp/

warp - A fast preprocessor for C and C++

https://github.com/facebookarchive/warp