Cross-platform functions
Most POSIX calls are supported on Unix and Windows. For areas that are different (e.g. scanning directories) BOINC supplies some generic functions with implementations for all platforms. Similar code may be available from other open-source projects.
LIST THEM
Most important: use gcc-3.0, at least for linking. This should limit the executable to GLIBC-2.2 symbols. Einstein@Home builds Apps on a Debian Sarge (3.1) system, using the gcc-3.0 from Woody. Take special care of which libs to link statically and which dynamically if you are using e.g. OpenGL.
For a portable build of the BOINC Core Client I found no better way than to make a clean Debian Woody installation (in a VMWare machine) from DVD, refusing all online updates (of the GLIBC). However this was quite some time ago, before BOINC switched to ssl, curl and zlib, I don't know if and how this still works.
The BOINC API is implemented in C++. Information about using it from C and FORTRAN is here. "; page_tail(); ?>