Port Knocker is a free, open-source port knocking client for Android developed by Ahsan Rabbani. It offers a simple and user-friendly interface to knock ports and launch applications. This app is similar to other port knocking apps but with a more visually appealing interface. It also includes a widget that allows you to quickly knock ports from your home screen.

One of the most useful features of Port Knocker is the ability to choose an application to launch after knocking. The app also requires media/storage permission for the import/export feature, allowing you to save your list of hosts and load them later. Overall, Port Knocker is a great tool for anyone who needs to knock ports on the go.

It is worth noting that the app is open-source, so if you encounter any bugs or have suggestions, you can report them on the developer's GitHub page.