[flavor8]

> One of the things I found frustrating about Nextdoor when I used it a year ago was that it defines the neighborhood for you.

That's not true. When you set up a neighborhood (if you are the first to do so) you can define the neighborhood house-by-house or by drawing a boundary. I don't know how they handle boundary disputes.

Regarding subgroups, you can create discussion groups within the neighborhood, and make access limited / invite only. So you could have a street by street set of groups, so each group would get general neighborhood plus street only content.