This version of Boost is under active development. The current version is 1.88.0.
A spiritual successor to Boost.FunctionTypes, Boost.CallableTraits is a header-only C++11 library for the compile-time inspection and manipulation of all 'callable' types. Additional support for C++17 features.
This Release
Boost.CallableTraits 
CallableTraits is a standalone C++11 header-only library for the inspection, synthesis, and decomposition of callable types. Language features added in later C++ standards are also supported.
The latest documentation is available here.
CallableTraits is released as part of the Boost C++ Libraries. Since it only depends on the standard library headers, you can also download it as a standalone library here.
Licensed under the Boost Software License, Version 1.0.