If you just need the overlay and achievements you can use the greenworks plugin.
construct.net/construct-2/addons/83/greenworks/documentation
If you have the video object in your project you better go with NWjs 0.29.4 and greenworks 13 (0.29.4).
If not, you can go up to NWjs 0.30.5 with greenworks 13 (0.30.4).
dl.nwjs.io
Versions greater than 0.30.5 are not supported yet, you should follow up on greenworks for updates
github.com/greenheartgames/greenworks/releases
After downloading the greenworks plugin from github you need to edit greenworks.js and remove 'lib' from the path on all the requires.
Example
change
greenworks = require('./lib/greenworks-osx64')
to
greenworks = require('./greenworks-osx64')