is there any repository to work on the project officially .....
even for designs themes
thanks exelent!!! Q2A rules
Q2A is not fully open source so there is no repository. But you can still make themes and submit them to the site, gidgreen will likely add it to the theme page.
Update: Q2A is open source now and the repo can be found on Github: http://github.com/q2a/question2answer
The source for ths project is at http://github.com/q2a/question2answer.