Launch this on any android device and the Ctrl_PC app on a PC you want to control, then select your PC's ip/port, hit connect from android, then allow the client from the PC app, and that's it. Start pushing buttons! Keyboard output will go to whatever window has focus, so you can test it with any app (notepad for example).
If you don't like the layout, change it. The button images, text, sizes, key bindings, even enable/disable any button at will to create your own custom control panel.