That made me wonder which megacorp did? Google published a lot of papers about their architecture, but no code. They have many open source projects modeled after internal tools (eg. bazel), but there's no search/GFS/mapreduce/monorepo OSS project from them. MS has VSCode, that's great, and they even open sourced .NET. But Azure is a full black box, just like (almost) every Windows component. (Finally calc.exe is OSS!)