Forum NoNonsense was made by camendesign, system stores all data in one RSS file per topic. Starting a new thread creates a new RSS feed, replying adds an item to the feed (there is also a option to add, can be used for updates/errata/corrections).

Users don't have to go through registration and e-mail confirmation and logging in each time. Forum asks you for a name and password when you post. This name and password forms a unique token, protecting the name from other people using it. Every time you want to post, just use the same name and password to keep the same name.

Forum is a example implementation.