Necklace of the Eye basically lets you modify traditional graphics, replacing the ASCII characters typical of the genre with tiles (pixelated graphics). It also lets you change the game's perspective, so you can play in first person or with an isometric perspective; it even lets you use the mouse on certain games.
This version of Necklace of the Eye includes the latest version of Hydra Slayer, a roguelike developed by the creator of this tool, in which you have to go to the nest of the hydras and cut off their heads. Besides being a great game, Hydra Slayer is the perfect game for trying some of the features in Necklace of the Eye.
Roguelikes can be complicated because of their rough graphics and interface, and that's exactly why Necklace of the Eye is such a useful tool. It's almost essential for anyone who wants to start playing this genre for the first time.