Special notice! While MC Tween is a nice extension and it will continue to work for AS1 and AS2 until the end of time, it is my duty to inform all citizens that I have switched the focus from further development on MC Tween to a new AS2 and AS3 extension, a real Class this time, called "caurina.transitions.Tweener" (or just Tweener). Tweener doesn't have as many features as MC Tween yet (for example, it doesn't have native filter tweens), and the documentation isn't 100% done, but it features a complete, more solid redesign with a few additional syntax features that were impossible to achieve with MC Tween. And it works the same for AS2 (including Flash Lite 2+) and AS3.
So, if you use MC Tween, or you're thinking about using it, I'd like to suggest you try Tweener instead. It follows all the principles of simplicity I tried to feature on MC Tween, but with a more powerful syntax. Tweener download, examples and documentation are available on Tweener's page. You can read more about this change on this blog post.
Thank you for your attention and sorry for this ugly box. And don't worry, this website will not be deleted or anything.
Notice for October 2008: also note that, if you are still interested in MC Tween and don't want to use class-based AS2 or AS3 solutions, Larry Benedict has taken the matter into his hands and updated MC Tween with some filter features that are not available in the latest version. You can read more about it (and download his version) here or here.
Extensions are optional methods and prototypes that add new features to MC Tween - feature that shouldn't usually be added to the core prototype because they're very specific.
Right now, I'm in the process of organizing extensions that should be put here and I'll update this page soon. In the meantime, if you have added a new feature to MC Tween and you think it's worth sharing it with others, please contact me and if it is good enough, I'll list it here with full credits.