Rich webpage or desktop app for a visual scripting language

I need a web page or desktop app for a visual programming language. I've included a PDF with a mockup and a Word doc with a description. This job is only for part one mentioned in the Word doc. We need this as quickly as possible and it's an internal only application so it's ok if it only works on one browser or if it requires silverlight. If we go the web page route we'd eventually like to take advantage of local storage to make it function while offline. I'm leaning towards making this a web page but if someone could pull off a desktop app a lot faster than any of the web page bids I will make it an app. If there's a technology you want to use for this project and you think it will help things get done faster, let me know. Nothing on the tech side here is set in stone. This could turn into a long term project so please let me know if phase two sounds interesting to you as well.