Its really too bad they decided to charge for this tool. It has some of the better graphs. I suspect someone will eventually come out with a good replacement. The data itself is nothing special almost any pc or phone will give you a list of AP it can see and the signal strength.
Your hardwired PC will need to connect to some device that has wireless network ability. There are some router that will display other devices nearby and there are some very fancy controllers that will attempt to triangulate between AP to find unauthorized router/ap. Still there always must be some device that has a radio that can receive all the broadcasts from the AP/ROUTER. There really is nothing that is as simple to use as inssider unfortunately