Check out live.geocaching.com -powered by Trackonfly!

Client and server platform for creating social applications utilizing GPS tracking.

• Portable - the mobile client runs on about everything with the required hardware: J2ME, Symbian, Win32, Windows mobile and Linux, Android (portable, not yet started)
• Map support for use of both online map server and local map data.

Some of the key features:

• Realtime locations of other users visible both on the mobile and web interface with chat support.
• Privacy options: (location available to public, friends, groups, selected invididuals, no-one)
• Allows integration of rich media, automatically geotagged.
• Touch screen support in the client.
• Collect tracks and mark places and shapes with the client, edit and view them on the web.
• Can track all sorts of external things too, like GPRS+GPS dongles, over TCP/IP or SMS.
• View objects stored on the web profile on the client (go to the spot and see how your future house fits there).
• With features tailored especially for geocaching - can do any other sport too :)
• ...and tons more.