This is one of my "designs" -- by which I mean, hacks :) -- for the DIY Stomp boxes Turkey Day competition (2012). The Blue Warbler is an optical vibe with an envelope circuit. It gives a watery vibe effect that can go from very subtle to deep throbs, and it reacts to your playing by speeding up, slowing down, creating rhythmic chaos, or stopping the effect altogether on short notes and then bringing in the effect gradually, all depending on how the controls are set and how you play. Despite the simple controls, there are a ton of tricks hiding in different settings. Plus it has a switch to go to a very class bias-modulated tremolo setting.
This was inspired by some circuits that have been floating around the DIY world for a while, but the envelope circuitry is unusual and possibly unique to this circuit in the way it interacts with the oscillator. Please see the thread on DIYSB for more information (and all due crediting!), and if you want to build one, visit my web site for the build documents.