Originally named wifijammer is a python script to interfere with Wifi access points and disrupt the network. This can be useful for penetration testing of your own network or if you suspect that spy wireless cams are around in your premises. There are online shops selling hardware wireless jammers too but they cost additional dollars, wifijammer is a simple application that anyone with a laptop and basic Linux knowledge can use. This kind of applications must be used with caution, you need to be careful not to interfere with a network that is not yours or risk arrest.
For this jammer program to work your wireless card needs to be able to inject packets to the network. You will have to learn your wireless card chipset, running the dmesg command in Linux will often show this information, or run lsusb if you are using a wireless USB dongle. With the obtained information you can then search on the Internet to find out if the card is suitable to run aircrack-ng or any other WPA cracking utility, if the wireless chipset can run a WPA cracking tool it means it is able to inject packets on a live network and it will work with wifijammer.
Wireless Access Point hacking
The jammer will automatically hop in between channels every second to determine all possible targets, after initial identification it will start jamming the signal sending constant deauthincation packets to the access point. This is a way to disassociate connected computers from the access point, cutting off their wireless access. wifijammer does not perform any denial service attack but a disconnection, the client is able to reconnect but as long as the attacks runs wifijammer keeps telling the access point to disconnect the client, with the same result than a denial of service attack without neededing that much bandwidth or resources. A benefit of getting a client to constantly re-authenticate to the access point is that it might be possible to capture the WPA2 handshake and gain access to the network.
There is another application to jam Wifi access points found in the WebSploit framework, wifijammer has the advantage of being a very small script that should run in any operating system where you can install Python.
If an access point has MAC filtering enabled you would have to spoof the MAC address of a client first before deauthentication packets are accepted. Having said that, expensive enterprise level wireless access points are able to detect continuous death requests and they will block you.