One’s been out for a while, but just got upgraded; one just came out. I’ll do the latter first. Images follow.

Here’s THAC0:

THAC0 Main Screen

You may wonder why the square dice which look like six-siders have 10s and 8s on them. It’s because every die looks like that. Not broken, but confusing UI. That screen is the result of rolling 7d10. You can touch the dice to move them around to sort them:

THAC0 Dice Moving

Which is a nifty feature. I like that. Alas, that’s about all I like. Here’s what I don’t like: the dice selection screen, which you access by touching the info button at the lower right. That’s a bad interface choice; it’s hard to touch and it’s not an obvious choice. The author should have used a real button. The resulting screen looks like this:

THAC0 Config Screen

Which is wrong in almost every way. From the top, we start with the True Random toggle. No explanation of what that means or the effects, and there’s something wrong with the slider anyway. Note the two-tone effect.

We then have the number of dice slider. This looks OK at first glance, but the number doesn’t update as you move the slider, so you have to guess at the positioning. Ooops, that’s six dice. Wait, that’s four dice. Aha, finally got five dice. Plus you can’t roll more than 10 dice at once.

I have nothing bad to say about the die type selector, although I will mention that I find the transparency of the panel visually unappealing.

Finally, “Shake to exit”? Unnecessary use of accelerometer.

So THAC0, while free, is clumsy and not very good. Fortunately, we have the D20 Gaming Dice Set to consider.

D20 Gaming Dice Set

There is absolutely nothing fancy about this die roller, but it’s really functional. You hit a number on the keypad, you hit the die type, you press roll, and you get the results. If you want percentile dice, you hit that button. It always defaults to the last die set you rolled, but you can clear that with the clear button. And the interface is obvious enough so that the screenshot gives you a reasonable chance at guessing all of that.

Non-obvious thing which I like: when you hit clear, it remembers the die type you rolled. So if you roll 7d10, then hit clear, then press the 6 key, you get 6d10.

Non-obvious thing which could be improved: if you roll 7d10, then hit the 2 key, you get 72d10. I think this is suboptimal — if you roll dice, it should be a pseudo-clear. You shouldn’t lose your dice spec, so you can keep hitting roll over and over, but you should get an effective clear if you hit a number button. This sort of mimics a calculator and would be quicker.

And finally, a thing that doesn’t matter: you can’t see the individual results for rolls of more than about 20 dice.

D20 Gaming Dice Set (big roll)

Not really a big flaw.

This app could use some polish — little stuff, like the vertical size of the Clear button being different than the 0 button. But it’s functional, which matters to me more. And some of the minor touches are great, like the gigantic font size for the result. Also, the author’s making improvements based on his experiences using the app: “It worked well, but after several great comments online, and a 5 hour D&D session last night, it was obvious there were some usability flaws.” And he’s responsive to email.

It costs 99 cents, unlike the other two dice apps on the App Store. But it’s worth a buck.