In university, we had to develop some software for a project using QNX (this was the 1990s). They had an interprocess messaging API that was simply awesome. You

In university, we had to develop some software for a project using QNX (this was the 1990s). They had an interprocess messaging API that was simply awesome. You just defined your data in a struct and used send() to transmit it to the other process, which used receive() to receive it. Easy to use and super fast - way easier than the IPC stuff that was available in Linux at the time.