The ErrHandler subsystem consists of classes and core functions for extending Visual FoxPro's error handling facilities, plus an accompanying demo application. The main benefits of this general-purpose facility are:
VFP 6.0 includes a number of powerful, built-in error handling features, and the FoxPro Foundation Classes (FFC) also include an Error Object class definition, which adds a customizable error-logging facility. The VFP/FFC Error Object class, however, is not universally accepted among the FoxPro community as the last word on error handling.
Doug Hennig has written a number of excellent articles on the subject of handling errors in VFP, and his Stonefield Database Toolkit includes classes supporting a different model of error handling from that of VFP's FFC. Doug makes a persuasive argument for the need to extend the model to multiple levels of error handling.
SpaceTime's ErrHandler classes were designed to address many of the same issues as these other approaches, but in a modular fashion minimizing the unrelated baggage that goes along with buying into an entire "application framework" like FFC or Stonefield. The ErrHandler foundation classes are derived from VFP's base classes, and they constitute a core layer (a very "thin" framework) upon which other utilities (such as Commander, Querier, Reporter, etc.), subsystems (e.g. Saver), and form-based applications (like XFormDBF and BTCrit) can be built.