I was going crazy trying to find a way to install the TL-WN8200ND USB Wi-Fi adapter on my Macbook Pro. It seems that Ralink only has drivers up to OS X 10.8, and TP-Link doesn’t even have any OS X drivers available. I finally found a solution in the InsanelyMac forum. Someone was nice enough to port both the drivers and the utility to Yosemite, and it works really well! You can find the archive in the previously mentioned InsanelyMac post, or you can download it from a personal mirror here. All you have to do is install and reboot.
UPDATE: theluxbay in the comments confirmed that it works on OS X Sierra. I have not tested as I no longer use the TP-Link adapter.
Here’s a screenshot of the utility running in Yosemite: