In the folder
app/code/core/Mage/Core/Block/Template there are 3 blocks declared.
Mage_Core_Block_Template_Facade- I found where this is used. It is used twice for the product view page in order to set some containers.
Mage_Core_Block_Template_Smarty- I found no reference of this. Anyway, this class just extends a core template. Most likely someone wanted to use smarty with magento and abandoned the idea.
Mage_Core_Block_Template_Zend- this has some methods in there. But again I did not find a use of it.
Are the last 2 blocks useful for something? My money is on "unfinished business" but I was wrong before (with this for example).
Any opinion on this? Anyone used these blocks before?