PrivTracker allows to share torrent files just with your friends, nobody else. Unlike public trackers, it shares peers only within a group which is using the same Announce URL. It really works like a private tracker, but can be generated with one click of a button.
The smaller the swarm, the less functional bittorrent is.
Instant private trackers for a handful of people kind of feels like its missing the entire point of how bittorrent works.
There’s already secure, serverless ways to share a file with just a handful of people, this seems like overkill.
EDIT: Not trying to be rude, it’s still a cool idea and well executed.