Almost everything I've done professionally is behind the wall of private intellectual property. It's an odd thing to spend decades doing work that you're proud of, but having nothing to show for it.
One of the few exceptions is a series of documents that I've written breaking down cryptographic and network protocols byte-by-byte. I'm always hearing from teachers, students, and fellow software developers who use these to learn, to fix, and to understand. I'm very proud of that.