Reef ball, Chaeto ball, Pod hotel.. whatever you want to call them on a given day.
. They can be seen in my pyrex thread and yeah thats what BigAl was referring too.
I originally designed it for my own tank. I wanted Chaeto in my biocube 14 but had no where to put it. And the pod hotel was born. Lots of ways to skin that cat, but nothing compares with pyrex. But basically a small ball of chaeto placed inside in the DT can look like a pod disco within 24-48 hours with all the little critters calling around in it.
I liken it to a ghost knife fish in a clear tube. For some reason it doesn't matter that its clear they feel safe. Eventually though they wander out and will either take up home in your rocks or get eaten.
Some people have used them like Al said just between the fuge and the display as an easy way to move a couple 1000 pods at a time without having to shake them out. Btw I dont' recomend trying to suck them up with a baster or even my pyrex droppers. Its an excercise in futitility. I used to empty my reef socks into a 5g tupperware and spend 3 hours trying to get all the pods out I can. Then I realized a live rock , one of my chaeto balls or a piece of sponge worked to get about 50% of them out. Considering the ones that are too small to see your getting plenty. You really need a clear dropper to appreciate the 1000's that are there in the filter socks.