Warhammer 40,000 41st Millennium Edition (not to be confused with 42nd Millennium Edition) is a fan made edition of 40K seeking to be the best of all editions of 40k mainly 5th (In fact it was originally called 5.5). 41st was started in 2019 and aims to make a version of 40k that closer resembles the older editions with some bits and pieces from all of them as well as add new factions (Some lore friendly some...not).

Warhammer 40,000 41st Millennium Edition Core Rules

Google Drive for all of the Books There's a fair few supplements here EG Titans and HH units for Marines and Chaos Marines