GNU/Linux is a free system--not just a collection of useful programs--because the GNU Project set out to make it one. RMS found, wrote, or found people to write everything required. FSF wrote essential components, such as the assembler and linker (you have no system without them). In the 90s the FSF had put together the whole system aside from the kernel, and they are still working on a kernel, the GNU Hurd, which runs on top of Mach.

See BSD/Linux.