There is a comment facility built into OJS where readers can discuss articles as part of the reading tools; however, if you want blogging or something more comprehensive, you'll need to install external software. Journal Setup step 5 has a tool to add links to the navigation bar, and you can enter HTML into most of the journal setup fields if you want to include links to an external application.
Open Journal Systems Team
Don't miss the First International PKP Scholarly Publishing Conference
July 11 - 13, 2007, Vancouver, BC, Canada