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Catkin is a meta build system (see design.ros2.org/ament for what is meta build system). Although it was developed as part of ROS framework, Catkin does NOT depend on ROS, meaning it can be installed without pulling any ROS libraries, it can run without ROS, and it can run against software that doesn't depend on ROS. So, as long as your software conforms to the minimum requirement of "Catkin package", you can build your software taking all advantages Catkin provides.
In order for a software to be "Catkin package"-conformant, it must:
have package.xml at the top level directory of your software.
have CMakeLists.txt at the top level dir, and inside of it have some speicific cmake macros defined in CMakeLists.txt.
Very minimum concrete example of CMakeLists.txt can look something like:
cmake_minimum_required(VERSION 3.0.2) project(your_package_name) find_package(catkin REQUIRED) catkin_package()