· http://www.gnu.org is the home of the GNU Project. From this site, you can download a staggering array of sophisticated free software applications. Among them is the GNU C library, which is part of every GNU/Linux system and contains many of the functions described in this book. The GNU Project site also provides information about how you can contribute to the development of the GNU/Linux system by writing code or documentation, by using free software, and by spreading the free software message.
· http://www.kernel.org is the primary site for distribution of the Linux kernel source code. For the trickiest and most technically detailed questions about how Linux works, the source code is the best place to look. See also the Documentation directory for explanation of the kernel internals.
· http://www.linuxhq.com also distributes Linux kernel sources, patches, and related information.
· http://gcc.gnu.org is the home of the GNU Compiler Collection (GCC). GCC is the primary compiler used on GNU/Linux systems, and it includes compilers for C, C++, Objective C, Java, Chill, and Fortran.
· http://www.gnome.org and http://www.kde.org are the homes of the two most popular GNU/Linux windowing environments, Gnome and KDE. If you plan to write an application with a graphical user interface, you should familiarize yourself with either or both.