I was looking through some of the games over at Gamejolt the other day and I noticed an interesting program at the top of the RPG section called the Encased RPG Engine. It's an engine designed for use with the game-making program Game Maker and it sets out the basic systems required to create a top-down, hack-and-slash RPG. Given that it comes with fully-functional inventory, melee combat and ranged combat systems, it looks like a perfect engine for people to use if they want to make anything remotely similar using Game Maker.
I gave the game that comes with the engine a play-through and it is pretty basic (as you'd expect) but everything seemed to work how it should. I have to admit that I was pretty impressed! In fact, if I was more experienced with Game Maker I'd be tempted to see what I could do with this engine because everything you need to get a game started is already there.