Do not use the Softpedia Gaming Keyboard Splitter on any PC with personal data, passwords, or sensitive work. Instead, use Interception Driver (open-source) or a hardware solution (USB switch box for two hosts). If you only need macro keys, buy a cheap programmable macropad (e.g., Elgato Stream Deck or a DIY Pro Micro board).
It works by filtering raw input from Human Interface Devices (HIDs) and redirecting keystrokes based on rules you set. softpedia gaming keyboard splitter