|Giffard Grenadine Syrup|
|De Kuyper Crème de Menthe|
|Triple sec liqueur|
|White overproof rum|
The amount of sugar in each liqueur and their temperature will impact their specific gravity and so how successfully they layer. This is more a test of patience and a steady hand than a drink.
A pousse-café is now a term for any multi-layered cocktail. The term originally seems to have been a general term for a mixture of liqueurs and/or spirits served after dinner, and most probably originated in France.