Designed for RPG Maker MV, may work with other engines. These are modern windows that work well for storefronts/shops - plain but blend well into many surroundings.  One version has a shelf inside the window where you can overlay items for sale if you want to. They're a little bit quirky so read usage instructions here: https://kokororeflections.com/rpg-maker-mv-autotile-windows/

More free stuff here: https://kokororeflections.com/category/free-stuff/