Every protocols under the sun that is in use today has an open source implementation used by closed source software and OSes. Why? Because if they didn't, those protocols wouldn't be popular nor used. From file types handling, to images, to audio driver code, TCP/IP libraries, every cryptography implementation, every webpage you visit; from top to bottom is mostly made of open-source code.
Unless you're talking about rockets' real time OS, even the most closed platforms would be made of roughly 50% open-source code.