Here is my list of the greatest Programs ever written:
1- The Linux kernel:
Not only does it power well over half the internet, it also powers 80% of the mobile devices on the planet (Android), as well as many consumer devices (TIVO, many routers, etc)
2- The GNU Compiler Collection (GCC).
The foundation on which the Linux kernel is based. GCC is a key component of the GNU toolchain. The Free Software Foundation (FSF) distributes GCC under the GNU General Public License (GNU GPL). GCC has played an important role in the growth of free software, as both a tool and an example.
3- The CERN web server and Web Browser.
While not popular themselves, they kicked off this whole World Wide Web thing and transformed the Internet from an academic curiosity to a basic utility that drives a big part of the economy.
Love it or hate it, I would add Windows 95. That was the OS that brought computing to the mainstream.
but nobody uses it today really
I think “Hello world” in C qualifies as well – how many programmers who have written how much software that’s *still* in use started with that program?