> [...]your engineering teams contacted me about some secret internal project and asked a large number of technical questions[...].
> [...]your engineers began asking me to make a number of changes[...]
Those are two cases where Intel asked Tanenbaum to work for free. First as consultant and then implementing custom code modifications.
Yes, not many people will charge for answering questions and maybe he thought that the changes requested by the Intel engineers were appropriate and useful for the project itself, but the fact remains that this work was valuable to Intel and required Tanenbaum to spend time on it.
I think it's debatable whether being contacted for information or asked to make changes to your open source project is "working for free". It's being asked to work on open source software, there's a difference.
