is DBus what I'm looking for?
apache, apache2, dbus, ipc
Solution
ZeroMQ provides all the features you ask for and then some. It's basically a "work no matter what" messaging system that'll take care of all the corner cases and subtleties in IPC messaging.
However, ZMQ and all the others like it are not applications - they're APIs you can use to create applications with. You would use ZMQ from whatever script your Apache is running (eg PHP backend).
Problem
I need an IPC system on Linux. My requirements are: - packet/message oriented - ability to handle both point-to-point and one-to-many communication - no hierarchy, there's no server and client - if one endpoint crashes, the others must be notified - good support from existing Linux distros - existence of a "bind" for Apache, for the purpose of creating dynamic pages sorted in order of importance (roughly). I don't need extreme performance, nor I will be sending high volume of data. I stumbled upon DBus, and it looks like a good candidate (it pecl::packages::dbus a good mechanism to let Apache access the DBUS?). But before diving deep in DBus documentation I'd like to hear some suggestions.