I can reply to all but SM forum.
1. As of this date, the code is freely available to them.
2. VB and IPB require payment to purchase a license.
3. I am not sure what the coders use to code them, but they are all php scripts and all will run at least on mysql. Not sure if any other db is supported, but I do not believe so.
www.phpbb.com www.vbulletin.com www.invisionboard.com are the links to these three. I am sure the developers will be sure to answer these questions if you prefer to get them from the horses mouth.