Hi RUC,
The Dashboard SDK provides developers to develop any type of Flex application or component into the dashboard designer. Please check the below link for more details on this.
Xcelsius SDK - Everything Xcelsius - The 'Xcelsius Gurus' Network
For more SDK development & tutorials check the below link in developer information:
SAP BusinessObjects Dashboards 4.1 – SAP Help Portal Page
Upgrading add-ons to Adobe Flex SDK 4.0 - Business Intelligence (BusinessObjects) - SCN Wiki
Hope this helps!!!
--SumanT