It's Deal of the Day time featuring Frog God Games' Tome of Adventure Design. Tome of Adventure Design is made up of four sections or 'books' as they are called in the tome. The first two are Matt Finch's Adventure Design Deskbooks.
I used these books a ton. Especially the first. These two were great toolboxes for constructing adventures and monsters.
The other two books included in the Tome of Adventure Design are Dungeon Design and Non-Dungeon Adventure Design. I've used this book more times than I can count. It's the best book on the market to get your imagination running to construct an adventure.
I think it's the best adventure design book on the market.
Normally the Tome of Adventure Design runs $21 for the PDF, but today it's only $8.40!