You may now play version 4.2 of Spacewar! (the earliest known digital computer game) online at http://www.masswerk.at/spacewar -- make sure to select the right version from the "Version"-menu at the top.
(There are also version 3.1 and version 4.1f, the latter being the version apparently run at the CHM.)
To my knowledge this is the first chance to play a version online that requires the PDP-1's hardware multiply-devide option.