Libmodule offers a small and simple C implementation of an actor library that aims to let developers easily create modular C projects in a way which is both simple and elegant.
Indeed, libmodule was heavily inspired by my own actor library experience with akka for its API.

Unsurprisingly, module is the core concept of libmodule architecture.
A module is an Actor that can listen on non-pubsub events too.
Frankly speaking, it is denoted by a M_MOD() macro plus a bunch of mandatory callbacks, eg:

#include <module/mod_easy.h>
#include <module/ctx.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>

M_MOD("Pippo");

static bool m_mod_on_eval(mod_t *mod) {
    /* Should module be started? */
    return true;
}

static bool m_mod_on_start(mod_t *mod) {
    /* Register STDIN fd */
    m_mod_src_register(mod, STDIN_FILENO, 0, NULL);
    return true;
}

static void m_mod_on_stop(mod_t *mod) {
    
}

static void m_mod_on_evt(m_mod_t *mod, const m_queue_t *const evts) {
    m_itr_foreach(evts, {
        m_evt_t *msg = m_itr_get(m_itr);
        switch (msg->type) {
        case M_SRC_TYPE_FD: {
            char c;
            read(msg->fd_evt->fd, &c, sizeof(char));
            switch (tolower(c)) {
                case 'q':
                    m_mod_log(mod, "Leaving...\n");
                    m_mod_tell(mod, mod, "ByeBye", 0);
                    break;
                default:
                    if (c != ' ' && c != '\n') {
                        m_mod_log(mod, "Pressed '%c'\n", c);
                    }
                    break;
            }
            break;
        }
        case M_SRC_TYPE_PS:
            if (strcmp((char *)msg->ps_evt->data, "ByeBye") == 0) {
                m_mod_log("Bye\n"):
                m_ctx_quit(0);
            }
            break;
        }
    }
}

In this example, a "Pippo" module is created and will echo chars from stdin until 'q' is pressed, exiting with 0.
Note that it does not even need a main function, as libmodule already provides a default one as a weak, thus overridable, symbol.

Yes, it is. Non-portable code is actually compile-time-plugins based.
On linux, libmodule's internal loop will use epoll, while on BSD and MacOS it will use kqueue.
On other OS, cmake will fallback at looking for libkqueue, a drop-in replacement for kqueue.

Finally, it heavily relies upon gcc attributes that may or may not be available for your compiler.

Yes, it is availabe at readthedocs.
There are some simple examples too, see Samples folder.
To see a real project using libmodule, see Clight and Clightd.

Libmodule, samples and tests are built and tested with github actions on ubuntu, freebsd, and macos.
Moreover, tests are executed and valgrind checked too.
Finally, a codeQL workflow ensures code quality.

We all know OOP is not a solution to every problem and C is still a beautiful and much used language.
Still, I admit to love code modularity that OOP enforces; moreover, I realized that I was using same code abstractions over and over in my C projects (both side projects and at my job).
So I thought that writing a library to achieve those same abstractions in a cleaner and simpler way was the right thing to do and could help some other dev.

You only need cmake to build libmodule on Linux and BSD/osx; it does not depend upon external software.
On other platforms, you will need libkqueue too.
To build, you only need to issue:

$ mkdir build
$ cd build
$ cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_LIBDIR=lib ../
$ make

Note that libmodule can also be built as static library, by passing -DSTATIC_MODULE=true parameter to cmake.

# make install

$ cpack -G RPM

And finally install generated RPM package.

$ cpack -G DEB

And finally install generated DEB package.

Libmodule will install a pkg-config script too: use it to link libmodule in your projects, or use "-lmodule" linker flag.
Please note that in order to test examples, there is no need to install the library.

For Archlinux users, Libmodule is available on AUR.

Libmodule is made available with a MIT license to encourage people to actually try it out and maybe use it inside their project, no matter if open or closed source.

Are you using libmodule in your project? Please let me know and I will gladly list it here.