Johannes has been submitting patches since shortly after the initial release, working on Key Value Coding, Key Value Observing, Key Value Binding, controllers and other things like the gcc 4.2.1 patch, C++ compatibility work and related Objective-C runtime fixes.
Rolf has been using Cocotron in the development of a Windows version of his application and has been submitting patches which reflect fine grained fixes allowing his code and nibs to be used unchanged across Mac OS X and Windows. He has been improving user interface layout and sizing so that fonts and nibs behave the same on both platforms, nib reading, user interface behavior and Foundation improvements.
Johannes and Rolf have been invaluable contributors, greatly improving the quality and functionality of the project. I am happy to give them repository access to streamline their contributions.