I think the point of the article is that you can do this without an app and the previous posters point is that app encourage low effort impersonal interactions instead of the personal community you want. So every app just quickly desolves into another nextdoor. Why don't you try asking the next neighbour you see to have a coffee, or do the same as the people in the article and take a camping chair and a coffee one Saturday morning and sit in front of your building?