Theme DIY (Do it yourself) at Symbian Freak is a freeware mobile application for Nokia S60 3rd Edition mobile devices that allows you to create and edit themes/skins directly on your mobile device without the need for a desktop computer.

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The software, after installation on your Nokia phone, allows you create up to 12 new themes, choose from 6 different colour templates, choose wallpaper background which can be stretched to size and rotated if you wish, choose music player background, choose to blur or fade background when in the menu, choose a ringtone for theme.
After this you can preview, save and then apply the new theme straight away to your phone. You can always re-edit theme later on.

Download this freeware Nokia application here