The Autotoolset package complements the GNU build system by providing automatic generation of legal notices, automatic generation of GNITS-standard directory trees, a rudimentary portability framework for C++ programs, support for writing portable software that uses both Fortran and C++, additional support for writing software documentation in Texinfo and LaTeX, and a manual introducing both Autotools and the GNU build system in a unified task-oriented manner.
cspot is a semantic annotator designed only for the C programming language. It is quite similar to cscope, but some more functionality. It can be used to find the declarations, definitions, and usages of functions, variables, macros, typedefs, and structs. It can also find visible identifiers at some position in the source, functions called by a function, global variables used by a function, usages of local variable declarations, unused global variables, unused function definitions, and more. Because it uses sparse, cspot knows more about semantics than cscope.
Auto-recompile is a small emacs add-on that allows you to fix compilation errors faster. It does this by continuously compiling the program you are working on while you are fixing problems. It eliminates the need to explicitly start a compilation for every fix you make, and manages your compilations and error lists in the background so that all you have to do is go from error to error and fix them until the program compiles.