Facing sharp criticism from academic computing experts, Blackboard Inc. announced Thursday what it calls a legally binding promise that it won't pursue patent lawsuits against users of open-source online classroom technology. An open-source group said it welcomed the move but noted a key caveat: It covers a number of named open-source projects, but technically leaves open the possibility future open-source initiatives that bundle proprietary software could be vulnerable. The announcement is the latest development in a case that has been closely followed in the information technology and education communities.