Simple Machines Forum, usually shortened to SMF, is free open source forum software in PHP. It is a long-established project and remains maintained.
How it models content
- Categories contain boards
- Boards contain topics and can be nested
- Topics contain messages
- Members with membergroups
Note the vocabulary. SMF says boards and messages where other systems say forums and posts. The structure is the same but the names differ, which matters when you are mapping fields between systems.
What moves cleanly
- Boards, topics and messages map onto other forum software without much trouble
- Members transfer, passwords generally do not
- Attachments need both the files and the database rows
- Modifications, SMF’s term for add-ons, leave data with no equivalent elsewhere