DTerm provides an efficient and easy-to-use debugging terminal for MacOS 9
and MacOS X programs, and other code.

Here are a few of the features of DTerm:

* One version for both Mac OS 9 CFM programs as well as
Mac OS X CFM and Mach-O programs.

* Displays results for each program in their own window.

* Time and date stamps every diagnostic message.

* Merge the contents of multiple windows into a single window to view
program interactions.

* DTerm library has no effect on running applications.

* Monitoring application can be created to send to end-users.

Yeah, that's great. So how does it work?

When the DTerm display application is not running, your program will be
unaffected by the DTerm library code.

When you want to view the diagnostic or debugging information from your
programs, simply launch DTerm, and the diagnostic information will be
displayed in a separate window for each program.

(http://www.austin-soft.com/DTerm/index.html)