Archi is built on an extensible plug-in framework (Eclipse). For the official Archi plug-ins, see the Archi Plug-ins page.
Here's a list of plug-ins created by other developers:
Archi Database-Plugin, a plug-in that stores models in a central repository. Created by Hervé Jouin.
CMDBuild for Archi is an extension to Archi developed at the University of Bologna and SIAE Rome that integrates CMDBuild, the Configuration and Management Database, with Archi. The CMDBuild newsletter introduces this plugin. Slides and videos (Italian) are also available.
A language pack is a third-party add-on that consists of a number of plug-ins that are added to the Archi installation in order to use Archi on non-English systems. To install a language pack ensure you have downloaded and installed the latest version of Archi. Then download the language pack and unzip the contents into the "plugins" folder of the Archi installation. Mac users will need to right-click on the Archi app and "Show Contents" to find the "plugins" folder in the app bundle.
(Please note that these screencasts are a little out of date now.)
Magic Connector - Using the Magic Connector to quickly draw connections and elements
Templates - Template Management in Archi
Navigator - Using the Navigator to visualise the model
Automatic Relationship Management (ARM) system - Creating relationships in nested elements
Format Painter - Copying and Pasting visual formatting
Dynamic Viewpoints - Using Dynamic Viewpoints
Archi lets you set the default colour for each ArchiMate element in Preferences, both for the colours used in the diagrams and in the application's user interface (tree and palette). You can also export and import these colour schemes. Gerben Wierda, the author of Mastering ArchiMate has helpfully provided the colour scheme that he uses for his models and in the book.
Download it here. In Archi, go to Preferences, "Colours and Fonts" and then click the "Import Scheme" button and import the file.