Private Forum Style Follow/Unfollow service?

Hey,
Does anyone know of anything that would allow you to add a small group of people (via email) to a project you are working on that you would appreciate their input on, and rather than emailing them updates and possibly annoying them, you add them to the topic and each time you post an update, they get notification mail and can ubsubscribe easily and can reply direct to the topic to give feedback and see other people's comments too?

Does Google hangouts or anything like that work in this way? I don't want them having to "sign up" to anything, just to email them a private link where they can observe the project?

Any help appreciated