Run this in Bash, navigate to http://localhost:1234/ and you're good to go.

#!/usr/bin/env bash
set -e
while true; do
  netcat -lp 1234 -e '
    read request_line
    resource=$(echo $request_line | cut -f2 -d" " | cut -c 2-)
    [ -n "$resource" ] || resource=.
    if [ -e "$resource" ]; then
      echo "HTTP/1.0 200 OK"
      if [ -d "$resource" ]; then
        echo "Content-Type: text/html"
        echo
        ls "$resource" | while read file; do
          if [ -d "$resource/$file" ]; then
            echo "<a href=\"$resource/$file/\">$file/</a><br />"
          else
            echo "<a href=\"$resource/$file\">$file</a><br />"
          fi
        done
      else
        echo
        cat $resource
      fi
    else
      echo "HTTP/1.0 404 Not Found"
      echo "Content-Type: text/plain"
      echo
      echo "Resource \"$resource\" not found."
    fi'
done

Of course this is very insecure, makes the browser guess content types, makes the browser infer content lengths and so forth. But it works (with most browsers)!