Sprose
Sprose is an embeddable programming language for plain text. Essentially, a given text file is parsed into a series of expressions. These expressions (S-expressions) are evaluated and their results are are inserted into the text in place of the expressions. The cool thing is that is all Sprose does. Literally everything else is completely customizable. Sprose expressions can be nested, create variables and namespaces, define functions, and anything else really.
npm install sprose
Example
A Sprose program needs two files, the text file which contains the expressions to evaluate and a JavaScript module which contains the functions and variables accessible by the text file.
This is a text file.
I can use (uppercase words in here).
moduleexports = { return sproseutil; };
This is a text file.
I can use WORDS IN HERE.