As recently announced in this thread on Story Games, and explained in greater detail in this thread on his own blog, Troy Costisick is trying out a new way of selling his RPGs:

I am going to offer customers the opportunity to purchase a subscription to my games rather than purchase each new game as it comes out. A subscription would include four books that would come out quarterly (every three months) and be complete, self-contained games. This is not a model where I create one “Core Rules” and release supplements every quarter. Each game is a unique individual and very fun to play.

He’s calling it DL-Quarterly, and you can find out more (and get a subscription) on the official product page.