Can I use… is an invaluable resource that we all (hopefully) use on a regular basis, but what if you have an existing codebase that you want to evaluate for browser support? You could go through it manually, but that could be a lot of work. Thankfully, someone has put together an app and a Node.js module that can crawl your CSS and list what will break in what browser.
This seems like a useful tool to point users to when you need some information about their browser following an error, to make debugging easier. It also seems to be in active development, so new features will be added over time.