Okay here goes.
4.0 includes extra add-ons such as this new "hair" shit. In my opinion, it looks more like some crazy spiky sticky hand flailing around. There is a new beta test for "joint textures" that is now compatible with 4.0 beta. So far, there is only little things available, for example "~" is the new "tab" (used to show the whole chat log) and "tab" now autocompletes names like in IRC. Some other new features include modmaker's items that actually include "triggers", e.g. the first person to touch "the flag" wins. There is also new sounds and music available that you can now turn off individually. There are some other options too- such as /opt hair 0, /opt grip 0, /opt tori|uke (shows character without particles/hair), 0 (mapped to screenshot for computers that don't have F buttons available), and new brackets for clan tags.
BAM