Metashell provides a compile-time debugger for debugging template instantiations and macro usage.

Metashell 3.0.0 is available

From the website:

Some of the major new features in 3.0.0:

• Profiling template instantiations
• Debugging template instantiations in expressions involving SFINAE
• Displaying preprocessed expressions

Commands for exploring the available headers (similar to the which and ls commands).
The full list of changes can be found here.

An online demo can be found at http://metashell.org/about/demo/

Installers can be downloaded from http://metashell.org/getting_metashell/installers#version-300