ucspi-ipc implements D. J. Bernstein's UCSPI protocol in the Unix domain, making it trivial to set up clients or servers on Unix sockets. ucspi- ipc comes with utilities using credential passing on Unix sockets, which are designed to act like a fine-grained and efficient sudo without the need for setuid programs.
Unifdef is useful for removing #ifdef'ed lines from a file while otherwise leaving the file alone. You specify which symbols are defined or undefined with -D and -U flags, and unifdef removes the corresponding ifdefs, and the enclosed code if appropriate. It's especially useful for removing those "#ifdef BROKEN" and "#ifdef PRIVATE" clauses from code before you release it. Unifdef acts on #if, #ifdef, #ifndef, #elif, #else, and #endif lines, and it knows only enough about C and C++ to know when one of these is inactive because it is inside a comment or a single or double quote.