If you use the Message module to notify users, then youYou can achieve what you want with Flag and Rules. To notify users, you can use the Message module. Here is a possible outline to make things work:
- Create a node Flag CommentedFollow.
- Create a Message type New comment.
- Create a Rule that launches when a user commented on a node:
- Check that the node's content type is Projects.
- Let the commenting user flag the node with Commented.
- Fetch all users thatwho flagged the node with CommentedFollow.
- Finally, loopLoop through this list and create a New comment message for every user in the list.
- (Bonus: depending on the text in your notification, you may want to set some of your message's fields. e.g. If you use Entity Reference, then you can refer to the user who commented and use his/her username in the message, for example.)
- Create a second Rule that launches when a user commented on a node:
- Check that the node's content type is Projects.
- Verify that the commenting user checked the checkbox for receiving notifications.
- Let the commenting user flag the node with Follow.
Assuming that the above steps are clear enough, I will not add an export of the RuleRules in question. By the way, if you want to notify users with an email, then you can forget about the Message module and simply replace the action(s) in the loop of the first Rule by "Send an email".