This is a fairly recent Kickstarter I backed, by Jeffrey Jones (he also does the Gary's Appendix books). I just got the final? PDF for it yesterday and I have to say I am blown away! It reminds me of the OLD Planet Algol blog, in a great way, I want to run/play this now. This is exactly what I have been looking for! It uses Old School Essentials for its chassis (one of my FAVORITE OSR editions), had the art, all done by the same artist (NO AI), it fantastic! I love Post Apocalyptic stuff AND Fantasy! Original Gamma World was my jam! And this delivers in gold! This is the first product in what is supposed to be more. Its a bestiary, and what a cool bestiary it is! Not just stat blocks but stuff a DM can use to inspire creative encounters. My only complaint is I want MORE NOW!! LOL
I just ended a 5E campaign, which will be my last 5E campaign, at least for the immediate future. I also backed Kevin Crawford's Ashes Without Number, its more gritty, less fantasy than this, but I can see using the monsters from Blood Sands in Ashes or using the tables in Ashes to supplement this, at least until more content for Blood Sands is released.
If you like Expedition to the Barrier Peaks, mixed Gamma World with AD&D back in the day, and love Science Fantasy! You need to pick this up when it is available to the general public!
Good Gaming -B.B.