In case you're not aware, Springtomize allows you to customize every aspect of iOS. You can do things such as increase the number of apps in the dock to 10, give the dock a cool coverflow effect, change the duration of the system-wide animations, remove page limits, customize the default animations, customize the lock screen, hide stock app icons and lots more.
According to Bigarella, Springtomize 3 is a completely new product, which has be rewritten from ground up, completely re-engineered, and will include support for iOS 7.
Here's a brief description of Springtomize 3 from Cydia:
Springtomize 3 is the ultimate utility for your iDevice! It's the only customization tweak you'll ever need. It features plenty of options to customize even the smallest aspect of your device(s). Every single option includes a brief explanation of its effect, making it very easy to use. The whole application has been localized in 20 different languages, so everyone will be able to use it without an issue.