Commenter Charles objects to HECS as
an exotic tax aimed at passing education costs to the next generation
Though until 2004 I thought that HECS could reasonably be classified as a tax, that analysis would have been disputed by the courts. Under the Constitution, there is a distinction between taxes and fees for services, and arguably HECS was a fee for service, in that the person who paid it became entitled to a specific service in return.
However, HECS had other attributes of a tax: it was set by the government, it went to the government, and was mostly collected by the Australian Taxation Office (up-front payments went direct to universities, but as money owed to the Commonwealth, with an adjustment to the government income of universities as a result). It made the Australian tax-welfare system mildly more progressive than it would otherwise have been.