Vialogues is an interesting site that reminds me a lot of Grockit Answers. This is a site where users can upload videos (not just YouTube) and then create discussions or "vialogues (video dialogues)" around it. A vialouge can be made public or private and even embedded into a site.
I highly recommend checking out Vialouges by clicking here!!
For a more detailed review check out Free Technology 4 Teachers.