SCore is a framework designed for writing flexible, extendable applications. Whereas most PHP apps are built monolithicly, score's event-based nature allows parts to be mixed and matched. For instance, the most famous collection of score extensions is the Shimmie image board, which includes user management, a wiki, a private messaging system, etc. But one could easily remove the image board bits and simply have a wiki with users and PMs; or one could replace it with a blog module; or one could have a blog which links to images on an image board, with no wiki or messaging, and so on and so on...
To learn about the innards of SCore, start with the High Level Overview.
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