Instant Update has basic support for plugins. You can extend functionality of Instant Update with plugins easily, if you know PHP. Plugins are based on hooks, to which you can attach your plugin's functions. Also, there are some predefined functions you can use from within your plugins to help you work with Instant Update.
Plugins are placed in manage/plugins/ folder, each plugin in separate folder. Each plugin has main file, named as plugin_name.plugin.php, which needs to follow some rules which can be seen in example plugin. Plugin can contain additional files.