If you can't find a suitable module/framework, Parallel::ForkManager could be used to maintain a pool of worker processes that you main server process can delegate to. At a minimum, the worker processes would need to be able to handle receiving any of the messages from you local server. Depending on how your code will interface with the ILS software, the workers may also need to be able to handle sending messages as well. Or the ILS software might be able to have it's own workers invoke the sending scripts directly. Or your send-side ILS interface could delegate to workers of it's own.

Forking is probably easier, especially if you use something like Parallel::ForkManager. Alternately, you could try to use threads. I can only assume that there is threads equivalent to Parallel::ForkManager you could use.

Is possible to to do this with out forking or threads by using IO::Select].