Skins are an alternative graphical interface for applications that support this feature.
They don't change the functionality of an application, just the look.
Below is a selection of common applications that support skins.
Below is a selection of skins, from the Aminet archives, supported by applications.
You may also need to install additional support for datatypes, this
is necessary if you are using skins with 'foreign' filetype formats such as .BMP.
You may also wish to design and create your own skins, so be sure to check out the Amiga Realm Software Directory.