I co-founded a startup called finesse.io, a cloud-based tool that enabled front-end designers to make changes to any website in the browser and save as their own version.
The idea for this was driven from the need for more tools for designers to be able to create and finesse their designs in context - in the browser, at different widths and with real content. After many years of working with developers and exploring different ways to communicate the designers' visions, one of the most successful methods for our team (at Conde Nast) was for the designers to get heavily involved in the CSS and have that control over responsive design and animation instead of describing it in other ways to a developer. This tool would sit alongside the many drag and drop tools that don't require any knowledge of CSS.
I was the design director and my co-founder and husband was the software developer. A complete MVP of this tool was built, allowing users to sign up and create projects. We had about 800 sign-ups in the first month and there seemed to be quite a bit of interest and need for something like this. Sadly we had to stop working on this, due to financial reasons.