decoupling indeed is a good idea

I believe it is a good idea.

What we want is that processes to not depend on other processes to be running. In our scenario the processes don't know about each other, they know only about the queues they use to either receive messages from or to post messages to.

Sounds to me like you want a message queue.

Evidently - that's what I said in the title, or didn't I?

My experience is limited to MQ Series

I've used MQ and would like to use it again but we don't have it and won't get it. If it was an option I would have listed it as number 5.

Oracle Advanced Queuing is a similar product. So this is one alternative to research.

This is why I posted this message...I had hoped for some feedback of people who have used it.

I donīt know Oracle AQ, I assume you have to spend money on it

It is part of Oracle. If you pay for Oracle you get AQ for free - that's why it is an option for us.

There are several free/open source products on the market

For the time being I would like to restict the discussions to the above listed options...

But many thanks anyway.