Designing Virtual Worlds book is free for limited time [pdf] Posted by judgementday on Tuesday August 17, 2021 @10:30AM from the mud.co.uk dept. https://mud.co.uk/richard/DesigningVirtualWorlds.pdf ( 2 comments | 7 points | on HN )
Dr. Bartle is still one of the best thinkers on this subject. Also, his personal website is delightfully 90s-esque.
https://mud.co.uk/richard/