Zigbee, zwave, WiFi, and Bluetooth, along with a number of others, are all communications protocols. So all those devices are “smart.“ For comparison of the ones that work with smartthings, see the community FAQ. It’s old, but it’s still accurate.
Also, I suggest you go to the quick browse lists in the community – created wiki, look down towards the bottom of that page for the project reports section, and then choose the first list, “get started.“ It should help answer many of your questions.
