Tail4win - Windows Tail »
OutputDebugString is a Windows debugging API. You can call it in all kinds of programming languages (VC/VB/C++ Builder/Delphi).
Hardcore Win32 developers are probably familiar with the OutputDebugString() API function that lets your program talk with a debugger. It's handier than having to create a logfile, and all the "real" debuggers can use it. The mechanism by which an application talks to the debugger is straightforward.
If the application has no debugger, the system debugger (like Tail4Win) displays the string. If the application has no debugger and the system debugger is not active, OutputDebugString does nothing.