Via DPF, it seems that Jim Anderton's Progressive party is no more, having been deregistered at its own request [PDF, p. 1009]. The party was only ever a vehicle for Anderton after he left the Alliance, but its demise marks the end of a chapter in our political history.
It also means there are now only five extra-Parliamentary registered parties. While these parties never get elected (thanks in part to the undemocratic 5% threshold), their number is a rough measure of the health of our democracy, of how involved and willing to participate people are. In the past year we've seen four deregistrations - the Worker's Party, Kiwi Party, New Citizen Party and Progressives - and only one new party (the Conservatives) gain registration. And with the Alliance and Democrats likely to disappear soon, that number will probably shrink further.