Tandem is open source software that enables web developers to visually create applications using tools similar to what you'd find in Sketch, photoshop, and other design tools.
Tandem can be used in parallel with a text editor, so developers an write code & visually manipulate their app in real time.
Tandem is also collaborative. Developers can share their workspace with designers who can then make visual edits without writing code, ensuring that the app being built is pixel perfect according to the designer's specifications.
Here's a link including more videos & descriptions:
Some keywords to play with that describe what Tandem is:
Design & Code, Web, Collaborative, Parallel, HTML, any programming language, Development, interactive development environment (IDE), visual programming, mirror, reflection, dimension, polyglot, layer
Also, I would love to see more logos around the concept of coding + design in parallel.