Wolfram Language Clones
Here's some projects that try to implement Wolfram Language in other programing languages.
Get Wolfram Language Free
Expreduce
Expreduce by Cory Walker https://github.com/corywalker/expreduce
It implements basic Wolfram Language in golang. 〔see Golang Tutorial〕
Mathics
here's another project that emulates Wolfram Language. This one, actually from a Wolfram employee Jan Pöschko, writen in mostly python.
Mathics is a free, open-source general-purpose computer algebra system featuring Mathematica-compatible syntax and functions. It is backed by highly extensible Python code, relying on SymPy for most mathematical tasks.
Symja
This one is one of the oldest, from at least 2002 i think. The project name changed several times. It was known as MathEclipse, and before that something else i forgot. Written in Java. The project's home page also changed several times over the decades. Written by Axel Kramer. (i don't recall if he is the original author or new coder that took over.)
Symja https://bitbucket.org/axelclk/symja_android_library/wiki/Home https://github.com/axkr/symja_android_library
Wolfram Language JS Frontend
https://github.com/JerryI/wolfram-js-frontend