There are several CAF alternatives with very different usages of C++ features:
* QP/C++: https://www.state-machine.com/qpcpp/
* SObjectizer: https://github.com/Stiffstream/sobjectizer
* actor-zeta: https://github.com/jinncrafters/actor-zeta
* rotor: https://github.com/basiliscos/cpp-rotor
At least two of them (QP/C++ and SObjectizer) are evolved and used for a longer time than CAF.