Is there an application with a graphical interface that can allow me to "see" devices on my network?

I am looking an application that will allow me to better monitor my network.

I was setting a static IP address on one of the devices on my home network, and when I entered in one address, it told me it was taken by a device I didn’t recognize. My network is encrypted so I wasn’t expecting for such a thing to happen. It could be a neighbor on our router or some other device in the house.