It's been five years (five Years!) Since Little White Bear Studios released TanZen onto the App Store. That's only about a month after the App Store came into being when you think about it.
To celebrate, the developer is making TanZen free for a limited time across the board. That means both versions of tangramy goodness, HD and not, are currently free to download. Even the free versions are free! Give it a look, I hear it's pretty good.