http://www.sheppardsoftware.com/states_experiment_drag-drop_Intermed_State15s_500.html

http://www.history.com/games.do

http://www.mrnussbaum.com/timedir.htm

http://www.digitalhistory.uh.edu/games/games.cfm

http://www.pbs.org/wnet/historyofus/tools/games.html