Crowd now ships with the Atlassian Plugin Framework 2. This gives developers lots of flexibility in extending Crowd and as more Atlassian applications migrate to version 2 you should see more similarities with configuration and development.
For an overview of the plugin framework and plugin development, please refer to
Currently Crowd has the following plugin points. A few of these are specific to Crowd, while others are more general across all Atlassian products.
The Crowd Google Apps connector is implemented as a plugin. Crowd customers get source-code access to both the plugin and Crowd itself, and can use the source in conjunction with the documentation to understand best practices for plugin development.
Once you have created your plugin, you should put the jar into the directory, a sub-directory of your shared Crowd home directory (or the main Crowd directory in versions prior to Crowd 3.0).
If you'd like to release your plugin to the world, please take a look at the guidelines in our Developer Network.