D&D Classics: Dungeon Masters Guide (2E)
Publisher: Wizards of the Coast
System: 2E
Type: Core
https://store.steampowered.com/app/1057900
D&D Classics: Player's Handbook (2E)
Publisher: Wizards of the Coast
System: 2E
Type: Core
https://store.steampowered.com/app/1057880
Mythic Monster #7: Inner Planes
Publisher: Legendary Games
System: Pathfinder RPG and D&D 3.5/ OGL
Type: Accessory
https://store.steampowered.com/app/731780
Nameless Horrors (CoC7E)
Publisher: Chaosium
System: Call of Cthulhu 7E
Type: Adventure
https://store.steampowered.com/app/647340