dckc
commented
3 years ago found it:
in May I discovered an interesting model in Trelgol Publishing: each work initially has a traditional per-copy price, but once its "world price" is met after so many copies are sold that way, the work is released to the public domain. -- https://www.madmode.com/2010/06/return-to-patronism.html
This book is under restricted distribution using a Market-Determined, Temporary, Distribution-Restriction (MDTDR) system (see http://www.trelgol.com) until October 31, 2010 at the latest. If you receive this book, you are asked not to copy it in any form (electronic or paper) until the temporary distribution-restriction lapses. If you have multiple users at an institution, you should either share a single copy using some form of digital library check-out, or buy multiple copies. The more copies purchased, the sooner the documentation can be released from this inconvenient distribution restriction. After October 31, 2010 this book may be freely copied in any format and used as source material for other books as long as acknowledgement of the original author is given. Your support of this temporary distribution restriction plays an essential role in allowing the author and others like him to produce more quality books and software -- https://web.mit.edu/dvp/Public/numpybook.pdf
Darn; I can't find that book with this license