There is also a 2 stage system, but cascade would be lower esspecially if you went all out(dont try this at home) and used low boiling point refrigerants.Like for instance a triple cascade system using R290 R170 and R50(propane ethane and methane).But don't count on making a system like that.
No the coaxial condenser I just explained how to build is a very efficient condenser as refrigerant is directly boiling on the condenser of the other system.