The Omni Group is sponsoring MacSparky this week, so I guess you can take this with a grain of salt, but I continue to be impressed with OmniFocus for the Web. For a web implementation of an iOS application, it has a lot more power than I expected. I didn't realize the way they were pulling it off.
They are running Objective-C and Swift on Mac servers that then output to the web. This isn't a simple web application. This is a Mac application driving to the internet. The OmniGroup explains in further detail at Inside OmniFocus.