Tomboy now (as of 05 June 2007) uses the Mono.Addins framework for extending Tomboy. If anyone gets time to explain the architecture of Tomboy Addins or how you'd write one, etc., please do so on this wiki page.
Extension Points (Classes)
Extend the following classes to extend Tomboy.
Extending this class allows you to do initialization when Tomboy starts up. Extend this class if you have something that should live on beyond just the lifespan of an individual note. As an example, the Tasks Addin extends this to allow TasksManager to exist during the entire Tomboy session (or at least while the Addin is alive).
Historically, this is almost exactly like a NotePlugin. Extend this class when your addin modifies behavior of individual notes.
TODO: Add more content
How to add your Add-in to the Community Repository
This is currently a draft, don't follow these instructions :P
The community repository is a git repo on gitorious. First setup an account on gitorious and clone the repository.
Now you can clone your gitorious repo to your local box.
git clone firstname.lastname@example.org:~<username>/tomboy/add-in-repo.git
Add your add-in in the right place in the repo. commit. Check the changes and push to your gitorious repo.
git add <files> git commit git show HEAD git push
Request a merge on gitorious so that one of the maintainers will merge your change back into the main repo.