Add-ons extend Freeplane features and/or look. Not all existing add-ons are hosted in this repository. There are other, user-contributed add-ons living in other repositories at Github and Bitbucket. You just should make sure:
- that your add-on is under version control, preferably publicly available.
- that your add-ons is listed on the add-on wiki page
Learn how to write your own add-ons from the add-on howto.