Currently, there are no services for listing Add-Ons/Apps? We are adding some capabilities (i.e. get Add-On by ID) in future releases, which is why you see this entity here.
If you can share your use-cases, we can try and attach them to the story we have going, but since that ship is already in flight ... it might be a tad late.
Hope that helps. =\
Thanks for the reply - the use case is for a Jive administrator to be able to review all addons/apps installed on the Jive organization by all of the organization's users