Though not exactly a plugin in and of itself, I'm working on a new module that will, if all goes well, enable rapid development of new ideas and new plugins like never before. The SandBox is exactly what it sounds like - it's a framework for playing with ideas. It's really just a very large and detailed template that is capable of switching between structure, progression, coordination, generative, and post-processing mode, so I can experiment with whatever type of module I choose. When SandBox is complete, it will have templates for every type of plugin designed to render the work of getting a new idea into music form as easy as possible. Without the hassle of having to set up a new plugin directory and rewrite the wrapping code for the module each time I have a new idea, I should be able to test way more concepts.
I'm hoping that the creation of the SandBox will mark a new phase in the development of mGen. I've always had a free-form development methodology, letting ideas come and go based on their applied effectiveness. Now, with the ability to see ideas in action with only a fraction of the development time, I hope to run through even more ideas in even less time - and have more of an applied focus than ever.
I'm already in the process of trying to decide which of my current ideas should be the first to play in the SandBox.