Is it possible to integrate Sitecore with external workflow engine (K2, Skelta), and if so, how to connect external workflow with Sitecore content item, and do i need to implement new interface in Sitecore (like workbox).
The reason why i need this, because current Sitecore workflow does not have all features that other workflow engines have, like escalating workflow items or parallel approval steps.
There are at least two ways. The most common way is to use Sitecore workflow actions to hand items off to the external workflow system. Another way is to implement the IWorkflowProvider and possibly related interfaces to abstract the external workflow engine completely. I personally have never tried either approach, so I can't provide any detail.