trackr! is a website designed to let you show your current location on Google Maps via GPS. To use trackr! you need a mobile phone with GPS capabilities or a GPS receiver. The site currently works with Windows Mobile 5 and 6 (PocketPC and Smartphone), Java phones with support for MIDP2.0 and the Blackberry.
The website also lets you track your friends. It is possible to create 'geofences' that allow you to receive an alert when a user enters and/or leaves a predefined area. This can be used, for example, to receive an alert when someone comes within a range of 5 miles of your current location.
Users of trackr! can put a map showing their current live position on their own website. It is also possible to save and share tracks. Each track has its own unique URL which can be shared with whoever you want.