The correspondence of the libraries with existing ones is:
Not really sure about this last one. But, It is just a package with some dummy samples and different likewise “hello world” code.
microROS/micro-ROS-Agent does not have equivalent or similar in ROS 2.
Regarding RCLC. This is just a fork with small modifications. We have some issues with this package while using our cross-compiling toolchain and building on windows. The intention of this fork, besides enabling the compilation, is to expand its implementation to include more of the ROS 2 concepts, thinking on services or timers.
However, this rclc expansion could be stopped, as a few days ago I found that RCLC is listed on Crystal roadmap, https://index.ros.org/doc/ros2/Roadmap/, so ideally we will embrace that future RCLC.
Anybody knows something about that RCLC on the roadmap?.
Hopefully, this answers your questions.