Autoconf, Automake and Libtool are packages for making your software more portable and to simplify building it--usually on someone else's system. Software portability and effective build systems are crucial aspects of modern software engineering practice. It is unlikely that a software project would be started today with the expectation that the software would run on only one platform. Hardware constraints may change the choice of platform, new customers with different kinds of systems may emerge or your vendor might introduce incompatible changes in newer versions of their operating system. In addition, tools that make building software easier and less error prone are valuable.
Autoconf is a tool that makes your packages more portable by performing tests to discover system characteristics before the package is compiled. Your source code can then adapt to these differences.
Automake is a tool for generating `Makefile's--descriptions of what to build--that conform to a number of standards. Automake substantially simplifies the process of describing the organization of a package and performs additional functions such as dependency tracking between source files.
Libtool is a command line interface to the compiler and linker that makes it easy to portably generate static and shared libraries, regardless of the platform it is running on.