Extras-devel is a repository for software used by developers whilst they are testing their own packages.
All of those that you've listed are also repositories, like extras-devel, but are just the generic extras repositories, so things should have gone through QA to get there.
Fremantle extras is the extras repository for Maemo5
Diablo - Maemo4.1
Chinook - Maemo4
etc etc

You don't want any of those other than Fremantle extras in your n900 repository list, or you'll be trying to add old software to your n900.