This version was released on January 27, 2004; this forum post explains the presence of a _spells.txt file that is not present in either v5b or v7b — it's probably a developer mistake.
This update comes with an update to the website as well as the forum, which moves from the Ankama Studio site to forum.dofus.com; the news item about this is available here and the closing of the old forum is available here. In this news item, it's mentioned that PIXEL magazine talks about the game in its early February 2004 issue — this CD-ROM might contain exclusive content about the game (maybe even a beta?).
As for the update itself, based on Liche's video of old screenshots #2, the character selection interface has changed, but the change may have happened before v6b.
A review of Dofus around the time of v6b is available here. This screenshot shows v6b with the use of the dofus+ tool, which allowed for extra features; this tool was developed by players.
(In this video by Liche), it's interesting to notice that the staff would push back one tile, and that equipment names seem to work the way they do in other games like Diablo 2, changing based on their stats. In the inventory, you can see weapons underneath the equipped gear — this could be a system for viewing inventory items. A guess: the Iop in the medallion has closed eyes; the animation of the Iop's eyes opening and closing may already have existed.
v6b had a bug with the Iop's hair color; this bug is mentioned by Liche in this video. The Iop's portrait medallion changed compared to previous versions (however, in beta v7b, the Iop goes back to the old medallion image). The Iop's skin up to v5b has short hair, whereas in v6b it seems to have long hair (v7b features the Iop with long hair). I suspect a date error on Liche's screenshots (Windows sometimes shows a modification date even when there wasn't one) — otherwise, there may have been a v6.1b or even v6.2b version, since fixing this bug would require a client patch.
You can see the maps making up Amakna during the v6b beta here; you can notice there are quite few maps — these maps only serve for wandering around, and some are very strongly inspired by what was planned for Duel (the map above the Amakna tavern where the business office is, for example). I think some of these maps were created well before the beta to get a preview of the environments that could be created, and consistency wasn't the goal, which would explain why very few decor elements are duplicated.
A screenshot of the multi-console is available here; it's indicated that this version added spells and combat effects.
Version v6b is the last version that uses the elements developed for the game's first trailer; after this version, Dofus gradually shifted toward deep changes that would put an end to the content planned before the beta and would completely transform the game.
