Decaflon

Hi to all. This is my first message. So take it easy if I am doing somethings wrong :)
I want a forum; simple, light, customizable. Is it too much? I know that there are thousands of forum software out there but comparising them using google is almost impossible. So I demand your help. I am going to talk about what features I want, but before that I know it is not easy to find all of those features (if not impossible) so I am ready to implement some of them by myself. But instead of starting from the begining I want to use an appropriate forum engine as a core. Because, most of the things will be same (like writing a post, categories, SEO etc). Let me go into details.

1. Registering, writing, replaying must be easy. Even when a nonmember try to write a post, by just choosing a username (little ajax) and writing a password two times he should be able to write a post (and become a member).

2. I want to keep my members history so that he should be able know what topics (and in each topic what messages) he read. In other words when he enters the forum he should be able to differentiate read messages from unread messages.

3. Treeview. Like a newsreader program (outlook express).

These are the main features that I want to have (or implement) however other useful but simple forum features are welcome too (like rating). By the way I prefer php/mysql, and a bit ajax would be cool. So what do you suggest?