There has been a lot of talk why Kunena switched to MooTools for our Javascript framework needs and why, in particular, with version 1.2.x that comes default with Joomla 1.5.19+ and 1.6.0.
I'd like to shine some light on the background of the ins and outs, clear up some confusion, and maybe provide some insight into why we believe this is one of the better decisions we have made since the start of Kunena.
When Kunena 1.0 started from the ashes of Fireboard, Joomlaboard, Simpleboard and the like, it came with Javascript based on the very popular jQuery framework. We enhanced and developed more and more features using jQuery, upgraded the libraries and kept moving forward with that direction.
More and more often we would get reports about broken Javascript and loss of the bbcode editor, quickreply and minimizer functionality on various sites. For almost a year, we tried to develop solutions to prevent our jQuery libraries from crashing with other jQuery libraries from various templates and third-party components. As it turns out jQuery (as all other frameworks would probably do) crash when on a given page two different versions of the same library are included.
So we wrote code with that between components like JomSocial and Kunena would result in the load of only a single copy of the libraries.
After dealing with these issues for many months and countless forum threads that last to this very day and after talking to various Joomla core developers and architects we came to the conclusion that we have been at this totally wrong for the longest time.