PhpBB

phpBB is a popular web-based forum package, written in open-source PHP. It is used by quite a few websites, large and small.

API docs

 * API docs (3.0.x)
 * API docs (3.1.x)

Source code and development

 * Source code
 * Development wiki
 * Bug tracker

Data import/export/backup/transfer

 * How to back up your phpBB forum
 * Transferring board to new host or domain
 * Create PDF copy of phpBB forum postings

Other links and references

 * Official site
 * Wikipedia article
 * What is wrong with phpBB? (discussion)