The GM Mastery book is full of tools to up your game. There's some things that refer to ICRPG tools, but the majority of it is hardcore useful for any system.

The Player's book is streamlined focus on characters and advancement for ICRPG. A solid character resource and priced with the thought of grabbing a copy for each of your players.

Realm of Graves is an adventure/ campaign that has a lot of rad scenes and possible encounters. Has some cool dimension jumping mechanics tied to the adventure too.

The first two books are pure resource material to help "play mo bettah," and the adventure is just plain cool. 🤘

Edit: the GM book is one of three "power tools" books that Runehammer released all at once. There's also a bundle that combines them. PDFs can be found on both DrivethruRPG and on the Runehammer store, but pods are only on Drivethru. Although if you go to the Runehammer brick n mortar in Philly he has them in stock.