As has been mentioned many times in the CIShell developer guide tutorials, the CIShell Specification is a valuable resource for understanding the CIShell platform. The OSGi Specification and Compendium (which unfortunately you must register to download), are also very relevant to CIShell development, especially the Metatype and Declarative Services Specification in the Compendium.
It may also be useful to look through the Network Workbench source code repository. Many of the algorithms in this repository use advanced techniques which are not fully described in this guide, such as including multiple algorithms in a plugin, or writing converters/validators for the CIShell conversion service.
The CIShell development team welcomes collaboration with other developers who wish to create tools based on CIShell. If you would like to get in direct contact with CIShell developers, please contact the Network Workbench project lead, Micah Linnemeier, at firstname.lastname@example.org, or contact Katy Borner, head of the Cyberinfrastructure for Network Science Center, at email@example.com.