Nookling Junction, T&T Mart, Super T&T, T.I.Y. and T&T Emporium are Animal Crossing: New Leaf's version of a general store (Nook's General Store in previous games). The Nookling General Stores begin as Nookling Junction and evolve over time to include expanded space and selection and longer hours.
In this shop you can buy general items that aren't category-specific. The selection of Tools, Wallpaper, Flooring and Furniture changes daily. You can also buy Medicine here. The store is run by Timmy and Tommy, the nephews of Tom Nook.
You can also buy Fortune Cookies here which unlock rare Nintendo Items.
This chart shows what each Nookling general store carries, and how each expansion is unlocked -- You must satisfy all of the requirements to get the expansion. An expansion causes the shop to be closed for one night.
Buy 100,000 Bells worth of items at T.I.Y.