"Knock on Ports" is an Android port knocking client developed by Alexander Yaburov. It is compatible with knockd, icmpKNOCK and other port knocking servers. The program allows users to send UDP/TCP/ICMP sequences, with support for both IPv4 and IPv6.

One of the standout features of "Knock on Ports" is its customizable content of UDP and ICMP packets. Users also have the ability to start another application after a knock, making it an efficient tool for power users. The program also offers Tasker integration, interpacket delays, sequence shortcuts, and a customizable widget.

Furthermore, data export/import is available for easy backup and restoration of settings. The program is completely free, open source, and does not contain any ads. Overall, "Knock on Ports" is a reliable and versatile port knocking client for Android users.