[eluser]Jon L[/eluser]
I think the ExpressionEngine forum module appears to be effective, light enough, speedy enough, etc, and I also like the default theme used here, so in my spare time I've been working on building up a forum of my own, but completely copying the forum appearance and functionality that you find here in the codeigniter forums. i'm not a designer, which is why I copied the theme appearance, but I'll have a designer redesign the application once I'm finished.
progress
I'd say I'm about 60% complete on the frontend (haven't worked on administrative portion yet), and I haven't built user management yet, though that's next on my to-do.
basic functionality
adding/removing categories and unlimited-recursion subcategories is functioning, as are threads, posts, and replies. i made an enhancement as well, so that when subcategories exist within a given category, they display above the thread list.
posts have properly functioning smileys and bbcode usage.
features
regarding bbcode, I found a user-contributed bbcode helper that I've used as a base, and then I extended it to support quote tags, code tags, and even advanced code tags for special geshi-syntax highlighting (so you can specify code="php", and you'll have php syntax highlighting).
another thing about my bbcode implementation, is that if you try to nest code tags here or in most other forum software, you'll find that nested code tags tend to break. i.e. - {code} stuff {code} nested bbcode example {/code} here {/code}
the proper intended functionality for a nested code tag, is for you to be able to reference the bbcode code tag itself as-is.
my implementation of the code tag parsing preserves nested code blocks without parsing :-)
to-do
I've still got a ways to go. Forum validation, error handling, administration; User component & administration for standalone forum operation; support for integrating the forum software into external applications and using external user tables (i.e. - attach the forum to a CMS or ecommerce software), alternate theme support, etc, but I'm happy with how far I've gotten
underlying code
btw, I've built my forum models in a way that the forum model itself calls upon 2 models, the first is for forum category access, the second is for post access. i've abstracted my models in this fashion so that the category model and post model can possibly be used for other purposes (I'm a huge fan of code re-use). additionally, both category and post models use the Nested Set library by Thunder (heavily modified - it was initially a Model, so I turned it into a Library. also, it didn't use native CI query generation, and there were a few other enhancements it needed, which I implemented).
performance
I'm happy with the # queries used to generate the forum display currently (single-digit queries atm), but I'm also aware that the finished product will obviously cause more queries to be generated, so I won't report on that yet, as it's nowhere near indicative of the final product's performance.
this is my first time building a forum, so scaling will be something interesting to measure as well, when complete.
