com.badlogic.gdx.scenes.scene2d.ui
Interfaces 
ClickListener
ComboBox.SelectionListener
List.SelectionListener
Slider.ValueChangedListener
TextField.OnscreenKeyboard
TextField.TextFieldListener
Classes 
Align
Button
Button.ButtonStyle
CheckBox
CheckBox.CheckBoxStyle
ComboBox
ComboBox.ComboBoxStyle
FlickScrollPane
Image
Label
Label.LabelStyle
List
List.ListStyle
ScrollPane
ScrollPane.ScrollPaneStyle
Skin
Skin.SkinData
Slider
Slider.SliderStyle
SplitPane
SplitPane.SplitPaneStyle
Stack
TextField
TextField.DefaultOnscreenKeyboard
TextField.TextFieldStyle
Widget
Window
Window.WindowStyle
Enums 
Image.Scaling