Behavly is for products whose users sign up and then go quiet. One snippet records what every signed-in user does (pages, clicks, scroll depth, rage clicks) and works out who they are on its own. Insights turn that into a signup funnel, engaged time, friction and who has gone quiet, with heatmaps painted over your real site. Build an audience from behaviour, in plain words if you like, and email those people from their own activity. Replies land in one inbox, and you see who came back.