VLC may go down as the greatest FOSS product in history. They've stated their mission since the beginning and 20 years later, are still flying that route. It's unbelievable how much money they've turned down to remain on their original mission.
I would definitely say VLC because just about everyone and their grandma knows about and probably use VLC on their computers/laptop even if they're not tech savvy. It's easy to download and install on windows, making it more accessible than Linux to the average computer user. Linux is definitely more impressive, but is used by way less people and is still mostly used in servers.
Edit:
I'm not including Android in the Linux count because I'm talking straight computer/laptop and not mobile devices. Don't know how many people would bother with VLC on android. I know I don't because I don't need it on my phone.
Yeah definitely Blender. It's not that hard to write a media player (hence why there are others like MPC). It's also not that hard to write a Unix kernel (hence why there are others like *BSD). A 3D modeller as complex as Blender though? I can easily imagine a world where it didn't exist and we were all stuck with Povray or whatever.
Kind of like the situation with CAD. (Though the FreeCAD 1.0 release seems to be finally vaguely usable based on my brief play with it so that might have changed.)
If there is something historical to talk about, it's how shit Windows was for both not providing basic functionality in a minimally serviceable media player. And worse, how it couldn't get the basics of OS-ing right in being susceptible to DLL hell and other similar issues.
In other platforms where such inadequacies were never present, VLC never became a big deal, because..VLC was never great in its own right.
The VLC project is marking this occasion with a really cool initiative called “LUNAR TIME CAPSULE”, where people can send their personal videos to the Moon aboard a video time capsule on the Griffin Lander, which is set for a late 2025 launch.
I mean the gesture is, I guess, nice but micro SD cards don't hold info for more than 10 years on earth, let alone in space with all the radiation, so it's entirely symbolic.