PortKnocker is a free Android application developed by Stephen Paine. It falls under the category of Utilities & Tools, and allows people running a port knock daemon to send TCP or UDP packets to specified ports. The application is based on the other app PortKnocking, but claims to be faster. It's important to note that this is not a hacking app. The app has a Chinese localization provided by NetDragon, which is a great feature for Chinese-speaking users. For more information, usage instructions, and the full change log, please refer to the website.

The application is straightforward and easy to use. Users can simply enter the IP address and port number(s), then select the protocol (TCP or UDP) to send the packet. The application can be useful for network administrators who need to test the connectivity of certain ports. Overall, PortKnocker is a useful application for those who require a TCP/UDP packet sender.