Migrate Extras extends Migrate to provide support for several contributed modules.
The best place to implement migration support for a contributed module is in that module, not in the Migrate or Migrate Extras modules. That way, the migration support is always self-consistent with the current module implementation - it's not practical for the migrate modules to keep up with changes to all other contrib modules. We are no longer adding support for other modules to Migrate Extras.
Migrate Extras 2.5 is now available. This is planned to be the final Migrate Extras release - the only work to be done with Migrate Extras going forward will be to port the contrib module support here directly to the respective supported modules.
Migrate 2: For compatibility between Drupal 6 and Drupal 7 implementations of Migrate V2, all features in core for Drupal 7 are supported by the Migrate V2 module itself on both 6 and 7. Notably, that means while CCK and filefield support were in migrate_extras for V1, they are in Migrate itself for Migrate V2.
Contrib modules with migration support - green checks indicate support is in Migrate Extras, N/A indicates a module which does not support that Drupal version, Requested indicates modules which have been asked for, Built-in indicates a module which has Migrate support built-in):
If you need to import content for a module not listed here, you can add a feature request to that module's issue queue, or you can use the included implementations as examples and write the extension yourself (submitting a patch to that module's issue queue). Creating these integrations is usually straight forward, but may require a proper understanding of a contrib module's APIs, along with their features and limitations. For more information on the Migrate API, see the Migrate documentation, particularly Handler classes - usually, supporting a contrib module is simply a matter of implementing an appropriate handler.