I noticed that on Windows the curses gem can be currently installed with just gem install curses.
Why is this not clearly written in the readme?

I was under the impression that a binary was not available for windows so I lost a lot of time looking for other ways to install it!

It should be more clear that on Windows all you have to do is "gem install curses".

Using the following Dockerfile:

FROM debian:stretch

RUN apt-get update && apt-get install -y git python libxml2 wget build-essential autoconf

RUN useradd -m -d /wasm wasm
USER wasm
WORKDIR /wasm

RUN git clone https://github.com/emscripten-core/emsdk.git && \
    cd emsdk && \
    ./emsdk install latest && \
    ./emsdk activate latest

ENV PATH="/wasm/emsdk:/wasm/emsdk/node

Simple-Web-Server is no longer under development, so it probably shouldn't be used anymore. Instead boost.beast includes functionality and examples to implement a "simple web server".