Trail Location aims to provide a drop-in replacement for (and eventually, extension of) CLLocationManager. Apple's Core Location is a good API, but it only provides locations from sources supported internally. For testing on the simulator, developing with an iPod touch, or even using the latest and greatest iPhone while at your desk, Core Location can be limiting for developers.
Trail Location adds the concept of a location Master to which location Sources may be added. A network Source and a network Sender are provided, making it easy to provide your location-based application with a source of test or demo data.
Until more documentation can be provided, start by taking a look at the "iPhone sample" and "Device Sends Location" sub-projects. Run the "iPhone sample" in the simulator and "Device Sends Location" on the device. By changing the center of the map on the device, the iPhone sample will change its location.
"iPhone Sample" uses a header search path to access the TLLocationManager.h, and then uses TLLocationManager just as one would normally use CLLocationManager. (A bug in the current developer tools also requires that an -all_load argument be passed to the linker so that a necessary CLLocation category is available to the client app.)