OMSP (or "one more slot package") is the name

Some are BG compatible, others are shiftable if you have AL.
The OFB shelf can be frustrating to work with, and I've had troubles with it myself. One of my lots was quite bugged after I saved with a sim on a shelf. The (very cute toddler) sim was gone, and I couldn't get him back. So the OFB shelf is currently used as a glass table with multiple slots in a hospital lot... and that's it.
Nowadays I only use OMSPs for posing sims and decoration. I've got the shiftable/angled AL set (there is both an AL set and BG set), and... hmm... in fact, I think I've got all those sets... The one-height OMSPs are perfect for their uses, while shiftable ones are a must when the other ones fail.
The black one in the first shiftable set is BG compatible, and will work much better than the OFB shelf. It only has one slot, in opposite to the OFB shelf, which has eight, and is annoying in the case of posing two or more sims together. It is also much safer to use. I've had no problems with disappearing sims after I came over these.