Boolean isCustomObject = true;
for(Schema.SObjectType objTyp : Schema.getGlobalDescribe().Values())
{
SObjectType objInfo = Schema.getGlobalDescribe().get(objTyp.getDescribe().getName());
if(objInfo != null) {
isCustomObject = objInfo.getDescribe().isCustom();
System.debug('Object Name = ' + objTyp.getDescribe().getLabel() + ' === Is Custom = ' + isCustomObject);
}
}