brent Solaar is open-source software replacing the proprietary Logitech software located on the Logitech USB sticks that come with new hardware devices.
It allows you to bind up to six hardware devices (keyboards, mice, periphials) to that USB keys software. You can usually have 6 devices connected per USB stick. As well keybindings, it controls which devices are connected. It can tell you if your batteries are low, show whether your connection to the device is encrypted or not, and do things like swap Functions keys and all.