I've been asked by some of the community users to write a guide for getting Steam overlay and achievements working under NW.Js, so here goes. I tested it on lin...
It's hard to guess without taking a look.
Make sure you didn't miss any file and that they are all in their right place (you can share a dir list, if you want me to take a look).
Make sure you wrote the right appid in the steam file and that there are no extra characters or spaces.
Make sure the events are actually trigger (print log), make sure the achievement ids are correct and that the achievements are all published (not waiting for review) on your steam app admin page.
You can also try and see if any errors are printed to the console log.
Ok. thanks again. I believe I didn't miss anything but have to check again... hmm