Borland Turbo Debugger
Turbo Debugger is a machine-level debugger for MS-DOS executables. It is a typical full-screen debugger with powerful capabilities for watching the execution of instructions, monitoring machine registers, etc. Later versions are able to step through source code that includes debug information, that was compiled with Borland compilers.
The software was originally a stand-alone product introduced in 1989 along with Turbo Assembler, but is most commonly found in the suite of Borland C++ products for MS-DOS. This suite, aimed at professional software developers, merged the Turbo C integrated development environment with several other tools such as a debugger, stand-alone assembler, profiler, etc.
Turbo Debugger is still around today, and is sold by Borland as part of their Turbo Assembler product.