puntoenv
Simple package that enables you to load .env files in to process.env and also do variable expansion in a predetermined order based on the NODE_ENV environment variable value.
envsub
envsub is envsubst for Node.js
path-interop
Provides path format conversion between Windows and Linux including path seperator conversion and environment variable expansion.
envex
Highly configurable env var launcher. Supports using async JS function calls and bash-style command expansion $(...)