I've been searching all morning but simply cannot find this darned thread!
It was someone's homemade rodent rack. The thing that made it different and what I wanted to look at was the supports/runners for the rodent tubs came out the front of the rack a little bit so when you pulled the tubs out, the extension would support the tub for you.
If anyone saved this thread, or you are the person who built this rodent rack, I'd really appreciate a link to it.