Every virtual file system is a file system plugin, Explorer Panel, Search UI, CheckSum , MultiRename are all different Application Extensions. And they all use the SDK. Everything you see in the Tools menu are from Extensions.
The SDK allows me to add new tools and features and integrate them into Multi Commander with less work. However there are some times the extension design has been a hinder. But those case are rare.
The SDK have not been public So only I have been able to use it. I been planing to release it publicly but doing that I need to clean it up, remove obsolete code and create a couple of sample and more.
And that is want I spent quite a bit of time on lately.
The first public version of the SDK is now out. It contains some sample plugins for FileSystemPlugins, Extending the MultiScript Language, Adding Tools that uses information provided by the API.
However the SDK can do a lot more. It can also create a UI that is show and use inside tab. But that is not included in this samples.
There is no documentation that describe every API call. but the documentation is heavily commented.
More information and download
For question about it use the forum or mail