Some systems allow two or more mice to be used at once as input devices. 16-bit era home computers such as the Amiga used this to allow computer games with two players interacting on the same computer. The same idea is sometimes used in collaborative software, e.g. to simulate a whiteboard that multiple users can draw on without passing a single mouse around.
Microsoft Windows, since Windows 98, has supported multiple simultaneous pointing devices. Because Windows only provides a single screen cursor, using more than one device at the same time generally results in seemingly random movements of the cursor. However, the advantage of this support lies not in simultaneous use, but in simultaneous availability for alternate use: for example, a laptop user editing a complex document might use a handheld mouse for drawing and manipulation of graphics, but when editing a section of text, use a built-in trackpad to allow movement of the cursor while keeping his hands on the keyboard. Windows' multiple-device support means that the second device is available for use without having to disconnect or disable the first.
DirectInput originally allowed access to multiple mice as separate devices, but Windows NT based systems could not make use of this. When Windows XP was introduced, it provided a feature called "Raw Input" that offers the ability to track multiple mice independently, allowing for programs that make use of separate mice. Though a program could, for example, draw multiple cursors if it was a fullscreen application, Windows still supports just one cursor and keyboard.
As of 2009, Linux distributions and other operating systems that use X.Org, such as OpenSolaris and FreeBSD, support unlimited numbers of cursors and keyboards through Multi-Pointer X.
There have also been propositions of having a single operator use two mice simultaneously as a more sophisticated means of controlling various graphics and multimedia applications.