Edit: To be clear, no XBox is necessary, that's another reason why people chose the Kinect.
Buy a Kinect2, if you have some time a used one is likely cheaper.
Then get the PC adapter kit which will let you hook it up to your PC like any old USB device.
There's an SDK and example software online, easily Googleable.
My main problem with these adapters is that they need to be plugged into the wall for power.
I prefer systems that use power via the USB so I can use it outside without an extension cord.
I'm pretty sure you nee to buy an actual Kinekt - Windows PC adapter. I researched this a few years ago and ended up with one. You will also need to get the Kinekt SDK I believe, to get the correct drivers.
https://www.amazon.ca/Microsoft-9J7-00001-Kinect-Adapter-Windows/dp/B00NMSHT7E
https://www.microsoft.com/en-ca/download/details.aspx?id=44561
Here's the Amazon link.
Why not just buy the official kinect to usb cable
http://www.amazon.com/Kinect-Adapter-Windows-xbox-one/dp/B00NMSHT7E