Yup, I rolled my own. I actually started work on this quite a while ago, but I put it aside for weeks at a time more than once, and it has also gone through one and a half complete rewrites. It makes a number of changes (improvements, in my opinion) from standard Futaba-inspired "rules," such as the email field, image files renamed by timecode, using Shift JIS (instead of Unicode), and the one-image-per-post rule, so that probably means that a lot of people won't like it. But oh well.

Please play with it, break it (but not so much my host gets pissed at me), whatever... Let me know what you think. I think at this moment it's "feature locked," as in I don't want to add any new features between now and the first public code release ('cept maybe sage-ing, which is already halfway implemented), merely squash bugs and oddities.

What you see here is its default skin. I actually posted some screenshots of it in http://nub.iichan.net/b/res/10314.html a couple of days ago, just to see folks' reaction... there wasn't one. (I was expecting a "WHAT IN HADES' NAME ARE YOU DOING, HEATHEN" flaming... mebbe I've overestimated the conservative temperaments of image board freaks.) I have also hobbled together a Futaba-ish skin basically by converting Wakaba's own futaba_style.pl; I'll take some screenshots and put 'em up in that thread.

http://pichan.org/thorn/index.php

Hmm, some first impressions on the interface:

• Far too hard to reply. I had to fumble around for quite a bit before I figured out what to do. Since you're not doing things Futaba-style anyway, and use a lot of Javascript, you really should switch to the 0ch-style of letting you reply directly from the front page without having to navigate to subpages.
• And also since you're using Javascript, there's no need for that unsightly huge list of file inputs. You can just add one more every time the user picks something in the last one.
• The reply count string is fairly unhelpful. I don't care how many replies there are in a thread, or how many are displayed - I only care how many are hidden, and I don't want to do maths to figure it out.
• The destination selector adds confusion and clutter - I can see why you'd want it, but there should be a more graceful way to add it. Most people don't care about it, and will only be confused by it.
• Sticky threads suck. But as long as you can only sticky them when creating them yourself they're probably a bit less annoying than 4chan's, though.
• If somebody actually wanted to put some effort into breaking that captcha, they'd probably succeed quite easily. A few image processing operations, and you'd have a very clear image to OCR, and since you only use numbers, the OCRing would be very easy. Colours do nothing in a captcha, for instance, since you can always filter them out trivially. They might even make the attacker's job easier.
• Dynamically built pages will eat your CPU pretty bad, should you ever end up running a popular site. A lot of sites out there suffer high loads only because they spend all their time building the same page over and over again.

Also, the timestamp filenames serve some quite important purposes for some people. If you download lots of image from an image board, the timestamps make a archiving and searching a lot easier. Also also, hardly any boards use Shift_JIS, except for this one and Japanese ones.

Also you'll want to consider supporting traditional 0ch tripcodes. They're not secure, but they are universal, and that counts for a lot.