This is the best Wireless monitoring software, I know of. I use it for planning and measuring of effective access-point and channel distribution. It is basically https://play.google.com/store/apps/details?id=com.vrem.wifianalyzer for my Notebook or PC.
The only similar software, I found in the Solus repositories is horst, which lacks the "scan window" for a quick overview of every WiFi in the neighborhood. Also the user experience and data presentation of Wevemon is absolutely excellent, especially if you are used to one of the similar Android Apps.
Yes, Wavemon is distributed under the GPLv3.