EDIT: the project renamed to OwnTracks
Here's a good, open and decentralized alternative which appeared recently:
A Google Latitude replacement based on MQTT
MQTTitude enables a device to periodically publish its location status to your MQTT broker. If you've previously used Latitude, you can think of this as a a decentralized Latitude.
Whether you want to keep track of your own location or that of a family member (with their consent, of course), MQTTitude will let you do that in a safe way. There are at least two components you'll want to use: one of our Apps, and an MQTT broker.
The app speaks to the broker. Other programs (we have a few for you, but you can create others yourself) speak to the broker as well. The smartphone app PUBlishes location data, and the other programs SUBscribe to that data. A program can store the data in a database, send it someplace (careful with that!), or simply discard it (which wouldn't really be useful now, would it?).
For the time being documentation is, ahem, a bit lacking, but you might find something useful on our development site.