FindMyCat – Open-Source Pet Tracker
Letting your domesticated cat roam the neighborhood is the worst thing you can do to the natural environment around you.  In N America, domestic cats are the most invasive species.  Why?  Because they absolutely destroy the local wildlife population.  Wonder why you don't see a ton of birds?  Because your cat is probably murdering them for recreation.This is a great example of engineers optimizing the wrong thing.