What does ww.wp.xz.cn use for its Extend section?

I’m looking for a file/downloads manager for my site. I’ve played around with 1/2 plugins here. Why isn’t the system which ww.wp.xz.cn use to handle its plugin section a plugin? lol The plugins I tested all seem to have their downsides and integration with other parts of WordPress were lacking.

For example, one offered tags, but these tags were independent from the internal tags.

Another allowed the setting of an author, but didn’t hook into users of the blog.