TinkerCell is a Computer-Aided Design software tool for Synthetic Biology. It combines visual interface with programming API (Python, Octave, C, Ruby) and allows users to share their code with each other via a central repository.
To read about the new updates, see the Blog (link on the side). For developers, the documents related to plug-ins and extensions might be useful (links on the side).
note: TinkerCell is no longer being developed actively. You are welcome to use it nonetheless. If you are a developer, you are most welcome to reuse part of the code or the entirety of the code in your own projects.