Extensibility Accelerator is basically a DIY (do it yourself) enablement package that allows the end-user to develop their own custom toolkit support sets/controls that aren't supported out-of-the-box in UFT. HP provides SDKs and as-is example templates to help the user get started on their own creation.
So, it can be looked at as two parts:
1) the Extensibility Accelerator software Add-in/toolkits/templates themselves, which can be found by running setup from the UFT full product installer media/files and selecting ''Add-in Extensibility and Web 2.0 Toolkits'' from the splash screen (Software_HP_UFT_12.02_MLU_T6510-15086DVD_WixExtensibility and ToolkitsExtensibility_Installation.htm):
In order to just use Extensibility Accelerator, you do NOT need any additional license. It is provided as-is (as far as the toolkit templates go), and you are free to install and develop as you wish.
2) the act of actually developing what you need:
If you decide what you want to accomplish is a bit too complicated for your developers given what is provided with Extensibility Accelerator, you can purchase additional developer services that can help you create your custom controls. To this point, HP provides ''Testing Extensibility'' as an independent SDK available as a separate purchase that requires its own license and support, it being an extended developer tool.