Audio tools face a set of uncommon user interface design and implementation challenges. These constraints make high quality interfaces within the open source realm particular difficult to execute on volunteer time. The challenges include producing a unique identity for the application, providing easy to use controls for the parameters of the application, and providing interesting ways to visualize the data within the application. Additionally, existing toolkits produce technical issues when embedding within plugin hosts. MRuby-Zest is a new toolkit that was build while the ZynAddSubFX user interface was rewritten. This toolkit possesses unique characteristics within open source toolkits which target the problems specific to audio applications.