Python is only one of many important open-source programs that are more than 20-years old.
Today, open-source software is everywhere but many peple still think of it as being relatively new. It's not. Open-source software actually goes back decades.
Before beginning our journey in the way-back machine though we should go over our terminology. "Open source," the phrase, only goes back to February 3, 1998. The phrase was deliberately chosen to separate the more pragmatic open-source supporters from the more idealistic "free software" community members. Gallons of ink and gigabytes of pixels has been spilled on debating the differences between these two, but for my purposes I'm talking about programs that qualify by either definition.
Both concepts were actually used long before proprietary software showed up. As Richard M. Stallman, (rms) free software's founder noted, "When I started working at the MIT Artificial Intelligence Lab in 1971, I became part of a software-sharing community that had existed for many years. Sharing of software was not limited to our particular community; it is as old as computers, just as sharing of recipes is as old as cooking."
That said, C remains a vital language in open-source circles and to do much with C you need a good, general purpose library. Over the decades the most important of these libraries has been glibc. Most of the credit for glibc's early success goes to Roland McGrath. By early 1988, McGrath had given what would become glibc, "a nearly complete set of ANSI C library functions." From this work would spring innumerable programs including Linux.
If glibc is important then gcc is vital. At its start, gcc only supported C. Today, it supports, to name but a few, C, C++, Objective C, Fortran, and Java. Almost every free software software project owes a debt of gratitude, and a lot of its foundation programming, to gcc.
6) GNU Emacs: 1984
Before there was gcc, the first major GNU program was the GNU Emacs programming editor. While I was never crazy about it—I'm a vi guy—I couldn't begin to count how many programs were written in GNU Emacs. Indeed some people assume that GNU Emacs was the first version of the editor. That isn't so. Emacs actually dates all the way back to 1972.
You could argue that these early versions were also free software, and I wouldn't fight with you about it. There's no question that such early versions as Multic Emacs and Gosling Emacs shared both ideas and code. GNU Emacs, though, became the version that would change the development world.
7) X Window System: 1983
At the same time that Emacs and gcc were starting to roll, others at MIT were working on the X Window System, a TCP/IP-based networking windowing system. No one knew it at the time but X Window would eventually become the basis for all important Linux and Unix interfaces, and the foundation for the Mac OS X interface.
9) First Berkeley Software Distribution (1BSD) Unix: March 9, 1978
The first open-source operating system wasn't Linux. That honor goes to, as Peter H. Salus wrote in A Quarter Century of UNIX, Bill Joy's first version of BSD Unix. When Unix first showed up in 1969, it was open source. Later it was closed, but BSD, the first fork, kept the free software flag flying. While BSD Unix never grabbed the headlines that Linux has, it's actually very important as well. Besides the BSD "distributions," such as FreeBSD, OpenBSD, and NetBSD, both Solaris and Mac OS X got their start from BSD Unix.
So, as you can see, open-source programs not only has a long history, it's also important in far more places than in software development. Since it's very start, free software has helped us in ways we didn't even know about.
So, the next time, someone says open-source software isn't good or trustworthy, just remind them that not only is it great, it has a better and longer track record than almost any proprietary software.