The GUI, showing blocks and items available to the player
Not Enough Items (NEI) is a useful mod added to Hexxit that lists all the items in the game and their recipes, and provides the ability to spawn those items in if you wish. It also has many features such as changing gamemode and time of day.
Delete Mode - When Shift-clicking an item, instead of moving the item (to hotbar and vice-versa), it will remove the item.
Creative Mode - Sets the player to creative and survival mode. Creative+ gives the player extra inventory slots and moves the armor to the side of the inventory.
Toggle Rain - Changes rain from on to off. In snowy biomes this produces or gets rid of snow.
Magnet Mode - When on, all items in a 16 block radius will be pulled towards the player. (Like Meteorite armor or the Coin of Fortune)
Set Time - There are options to set the time to dawn, noon, dusk, and midnight.
Heal Player - Sets the player at full health and hunger when clicked.
Search Bar - Allows for the searching of any item or block in the game. Double clicking the search bar highlights possible items in the inventory.
"R" Key - Gives the recipe for the selected block or item (if there is any).
Note: Default Keyboard Control layout uses the "R" Key to Sort Inventory. Using the "R" Key or Selecting an item in Recipe mode will sort your inventory.
"U" Key - Shows the recipes that the selected block or item is used in (if there is any).
"O" Key - Enables and disables the NEI interface.
Some way to 'craft' items is not recognized by NEI (like Tinkers' Construct tool station) will not be listed in NEI.