I think of a dumbwaiter as being small device like an elevator to pass items from one level t another level. Someone here installed something like this to pass food and drinks from the galley to the FB. Can't remember who it was, but it looked great! I hope he sees this thread.
If you're looking for a bar that rises out of a deadspace under the galley counter at the push of a button, I think that's what PineappleGirl installed in their Present 35. I never saw the final product, but what I saw in the process of being installed looked great. Paging PG...