Zwift is a great addition to your treadmill training, connecting you with a community of runners and cyclists, and letting you pick from a variety of virtual courses to give your indoor training some variety.
To get started, all you need is a Zwift RunPod and the Zwift app. The RunPod is a cadence sensor that attaches to your running shoe and tracks each step. You can use just about any treadmill (Zwift has some handy recommendations for choosing the right one), but there's also an increasing number of smart treadmills that can connect with Zwift directly. Check out the full list of supported treadmills.