Twitter

Twitter is a simply communication tools with rapid responsiveness. It could be used as Business tool also, because it would be able to reach far beyond your inner circle of friends. Twitter also has many other applications being developed. However, it limited to 140 characters per Tweet, and limited functionality, such as find people, send brief messages, direct replies, etc. In my opinion, It would not be a great tool for class discussion, because the discussion will also involve people from the other classes or communities.

Blackboard Discussion on the other hand has no text limit, However, it won't be a great business tool because people in that discussion group is limited, also it does not have many other applications being developed, but the good things is people would be able to reply directly to that post within that group and that keeps the whole class together.

In Class Discussion also is a freedom of speech place, which means no limitation to how many words that one should say. One thing is very similar to Twitter, which is one could receive an immediate response from someone. It also fits one class together and keeps the dicussion only within those group members.