It will come as a surprise to no one who knows me ... I wrote my own.

More, I created a system wherein people can register, and then whenever someone is travelling they can tell the system and it automatically emails everyone they know who is close to the destination.

I'm the only one who uses it, although there are a few hundred people on it, so I basically just use it as my geographical address book.

I also put landmarks, museums, and other places I might like to visit. When I tell it where I'm going it then sends me email to remind me of them.