MyBB is free, open source forum software written in PHP and using MySQL. It has been around a long time and is still maintained.
How it models content
- Forums, which can be nested
- Threads inside forums
- Posts inside threads
- Users with groups and permissions
Straightforward structure with no surprises, which is why moving in and out of MyBB is usually easier than with more elaborate systems.
Themes and plugins
Theming works through templates stored in the database rather than files on disk. That makes edits quick and makes them easy to lose track of. If a MyBB install looks heavily customised, check the templates before assuming the appearance comes from a theme folder.
What moves cleanly
- Threads, posts and users transfer well to other forum software
- Attachments need the files as well as the database records
- BBCode markup often needs converting if the destination expects something else
- Plugin data usually has no equivalent