What I never understand is under open source license of any sort, do people generally expect credentials? Fame or money or both, do you think you should get at least one? Just a question, no opinion on Mr Tanenbaum's letter per se.

The BSD licence that MINIX 3 uses actually requires giving credit:

Copyright (c) 1987, 1997, 2006, Vrije Universiteit, Amsterdam, The Netherlands All rights reserved. Redistribution and use of the MINIX 3 operating system in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

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Source: https://github.com/Stichting-MINIX-Research-Foundation/minix...