xdotool
lets you send X-events.

xmacroplay/xmacrorec2
lets you record a list of X-events in a file
and replay them.

xab
lets you define words which are send
instead of other words during typing.

xev
Outputs all events which the window gets.

xremote
a utility for grabbing the mouse and keyboard of another screen

xtrlock
lock utility.