Format MM/DD/YYYY :
TEXT(MONTH(Date__c))+ "/" + TEXT(DAY(Date__c))+ "/" + TEXT(YEAR(Date__c))
Format DD/MM/YYYY :
TEXT(DAY(Date__c))+ "/" +TEXT(MONTH(Date__c))+ "/" +TEXT(YEAR(Date__c))
Format YYMMDD :
formatRIGHT(TEXT(YEAR(DATEVALUE(Date__c))),2) + "" +LPAD(TEXT(MONTH(DATEVALUE(Date__c) )),2,"0") + "" +LPAD(TEXT(DAY(DATEVALUE(Date__c))),2,"0")
Format YY/MM/DD :
formatRIGHT(TEXT(YEAR(DATEVALUE(Date__c))),2) + "/" +LPAD(TEXT(MONTH(DATEVALUE(Date__c))),2,"0") + "/" +LPAD(TEXT(DAY(DATEVALUE(Date__c))),2,"0")
Format YYYY/MM/DD :
TEXT(YEAR(DATEVALUE(Date__c) ))+ "/" +TEXT(MONTH(DATEVALUE(Date__c) ))+ "/" +TEXT(DAY(DATEVALUE(Date__c)))