Matlab: it takes way too much Fortran code to solve Ax=b
Octave: Matlab is closed-source (and expensive)
Julia: Matlab was designed by people who knew a lot more about numerical analysis than programming language design
Python + SciPy: you don't actually need a whole new language just to solve Ax=b
TeX: it's taking too long for people to typeset my books
We're GNU. We don't care so much about the closed/open distinction as we care about the free/non-free distinction. The goal is that you should be able to run and share your code without anyone's permission.
I'm also planning to make Octave expensive as well. :-) Hopefully I'll manage to get this Octave startup off the ground.
https://www.gnu.org/philosophy/open-source-misses-the-point....
In the late 1970s, Donald Knuth was revising the second volume of his multivolume magnum opus The Art of Computer Programming, got the galleys, looked at them, and said (approximately) "blecch"! He had just received his first samples from the new typesetting system of the publisher's, and its quality was so far below that of the first edition of Volume 2 that he couldn't stand it.
Markdown: XML sucks for writing things by hand
R: because Perl isn't dangerous enough
TOML: Because INI files, JSON and YAML parsers are either too hard to read or write sane parsers for (It's not a language, but hey data formats are people too.)
Elixir: Because I want to be a Ruby hipster and an Erlang hipster at the same time (I'm only a lowly Ruby hipster.)