I found out how to remap Caps Lock and S to something else: CapsLock &:: ...
But how can I have a combination with three keys like CTRL, ALT and S?
Per the official AutoHotKey Mouse, Joystick and Keyboard Shortcuts documentation:
^!s::Send foo
Note, however, this only works with multiple modifier keys (Ctrl, Shift, Alt). Regarding "other" three key combinations, the documentation currently states:
Combinations of three or more keys are not supported. Combinations which your keyboard hardware supports can usually be detected by using #If and GetKeyState, but the results may be inconsistent.
It goes on to give this example of how this last part might be accomplished:
; Press AppsKey and Alt in any order, then slash (/).
#if GetKeyState("AppsKey", "P")
Alt & /::MsgBox Hotkey activated.
; If the keys are swapped, Alt must be pressed first (use one at a time):
#if GetKeyState("Alt", "P")
AppsKey & /::MsgBox Hotkey activated.
; [ & ] & \::
#if GetKeyState("[") && GetKeyState("]")
\::MsgBox