Gimp is another well-known tool I use somewhat frequently. I'm not a graphics designer so perhaps Adobe's tools are better, but for the kinds of tasks developers find themselves doing I find Gimp more than adequate. Not to mention I can run it on any platform, which is nice.
Open source compilers are so good that for the most part people don't even bother with commercial compilers. I've been around the block enough times to remember when that was not the case.
Linux/BSD. Unless I needed a tool for my livelihood requiring Windows, why would I ever buy it? Mac OS I get because people are buying the machine and the OS is free - otherwise there's not much point to buying it either.
QEMU and Xen are other successes in the virtualization space.
The only place open source isn't faring as well is in the mobile space - at least not that I'm aware of. Yes there are a lot of mobile projects on GitHub, but I don't know of people using Open Source mobile apps.
For text manipulation (including editing), GNU Emacs (which also was superior to and eventually beat out commercial Emacs like Gosling Emacs [ https://en.wikipedia.org/wiki/Gosling_Emacs ]) is far more powerful than any commercial offerings.
As an operating system, Linux seems to be well-established as the server and scientific/supercomputer OS.
Maybe OpenZFS over commercial RAID offerings?