There is a great variety of USB switches. Some switches are developed for two computers to share one USB device. Such switches are targeted on home users sharing a printer or a scanner. Some switches can support up to four computers and have an outgoing port for one USB device. And some switches can let you share four USB devices among four computers.
USB hub is exactly the opposite of USB switch. Thanks to a hub one computer can access lots of devices without them being connected to it. This is very handy when you need to work with multiple devices without any delays and interruptions.
USB over ethernet software can help you share USB devices among many computers without any additional hardware.