How difficult is it developing an interface for kids as opposed to adults?

That's hard to say. I sadly must admit to not having much in the way of "true" application development. No Windows or Mac API, GTK+ or Qt. Aside from doing Tux Paint, I do games. Games for the web (HTML, C, CGIs and PHP scripts, etc.) Games for cellphones (Java/J2ME and C/BREW). Games for Linux (C with SDL, like Tux Paint). I've also done plenty of other Web development. As my time becomes more 'copious', I'd like to sit down and finally learn wxWidgets. And/or GTK+. And/or Qt. I guess I just need a good reason to, and that hasn't come up in my professional life yet.

What were some of the key changes to the latest version of Tux Paint?

Honestly, the last version was more of a bug-fix release, it was the previous version that was packed with new features, and new dependencies. Those dependencies required some changes to get things running well on Mac, Windows and BeOS, which finally settled, so I pushed out the bug-fix release.

The last big changes include a "pick any color" dialog, a dozen new Magic tools, and support for the Pango text rendering library, which allows us to finally display more complex languages properly, such as Arabic. I also pulled out all of the previous Magic tools and created a new plug-in API, that allows people to create and test their own Magic tools a lot more quickly and easily.

As kids can be so unpredictable, were there any unexpected features in Tux Paint that you were sure would work well that didn't, or vice versa?

It's hard to say what works and what doesn't with the Kids, since it's such a rare occasion that I get to watch kids using it. I see their end results, but I have no idea how much fun or frustration they had during the process.

I hear plenty of kudos, and complaints, from schools. Schools have found that they really need Open and Save File dialogs, which I specifically avoided (part of the PalmOS inspiration). Schools also find that kids need to go back and correct text they've added to the picture, which is impossible without either using the Undo option, or erasing the text manually. Fortunately, work will be done on both of these fronts, thanks to Google's Summer of Code program.

What does Tux Paint have from a development and user perspective that KidPix doesn't?

I've used KidPix twice. Once on an old black-and-white Mac in the mid-1990s, and once using some Flash demo version, a few years after I started Tux Paint.

I can really only base my comparison on screenshots I've seen, and comments I've heard, mostly from educators. From the user interface perspective, I find Kid Pix a little too messy. Even as a kid, I've found "wacky" kid stuff annoying, and I suppose that still holds true. Capability-wise, I believe Tux Paint is a lot more extensible. Adding new brushes, starters, stamps, and even Magic tools is well-documented.

The one thing I think Tux Paint lacks is an animation/presentation system.

I recently added a "Slideshow" interface, but it's really just a stop-gap. I envision a completely new, separate tool for creating animations, that would integrate itself with Tux Paint (that is, make your saved pictures available). If I were to sit down and design it, I'd probably look at modern animation programs meant for adults and professionals, and boil it down the same way I did with Tux Paint.

Does proprietary educational software always have the kid's education at heart, or is making money the chief motivator?

Not being involved in any proprietary educational software development, I definitely don't feel like I can answer that. What I have seen is a lot of complaints about the state of Tux Paint's "competitors," when it comes to UI design and, more importantly, actually being usable in school situations (over networks, on terminal server/thin client setups, etc.) And that's without taking into account the fact that many are platform-specific (read: Windows only).

Do many adults use Tux Paint?

Certainly. The Tux Paint online gallery exhibits a ton of work by adults of all ages. Some of it is incredibly well-done, which goes to show how capable of a drawing tool Tux Paint can be, in the right hands.