[Plug and play for bare hard drives](http://gizmodo.com/gadgets/hard-drive/hdd-dock-plugs-bare-sata-drives-like-nes-cartridges-312747.php).
It’s always been a great annoyance that bare (i.e., designed for installing inside your computer) hard drives are so cheap, but buying an enclosure and swapping them around is tedious, and external drives are much more expensive. This looks like a good middle ground.