Does there exist some framework for parallel editing XML-document on a web-page through AJAX?
I need a shared whiteboard, where I and other people can draw and see that draw others in real time ("live" mode).
Modern browsers support SVG, event-source and other useful things, and if such a framework exists, make such a board should simply.
If not, what are the implementation on Operational Transformation and what engines for parallel connection of several clients over HTTP is best to use?
The keyword here is "collaborative editing" which is used extensively in Google Docs.
There's more info on the subject here: http://en.wikipedia.org/wiki/Collaborative_real-time_editor
Google Wave (which I believe was Google's first collaborative editing venture) is now open source: http://en.wikipedia.org/wiki/Google_Wave#Open_source
A bit of further reading should provide the answers you're looking for.