Looking for a program similar to Alfred and Keyboard Maestro
Keyboard Maestro can do this in a number of ways.  An entirely extensible way is to make a sequence of self-disabling macros, something like this:

Macro: First Command Key
Trigger: Device Key Command Key
Actions:
Disable Macro "First Command Key"
Enable "Second Command Key"
Pause 3 Seconds &lt;- adjust as necessary
Disable Macro "Second Command Key"
Enable Macro "First Command Key"


and then

Macro: Second Command Key
Trigger: Device Key Command Key
Actions:
Disable Macro "Second Command Key"
Enable "Second Command First Option Key"
Pause 3 Seconds &lt;- adjust as necessary
Disable Macro "Second Command First Option Key"


and then

Macro: Second Command First Option Key
Trigger: Device Key Option Key
Actions:
Disable Macro "Second Command First Option Key"
Enable "Second Command Second Option Key"
Pause 3 Seconds &lt;- adjust as necessary
Disable Macro "Second Command Second Option Key"


and then

Macro: Second Command Second Option Key
Trigger: Device Key Option Key
Actions:
Disable Macro "Second Command Second Option Key"
Perform whatever actions desired.


etc

It'll take a couple minutes to set up, but you can configure it any way you like.