Obvious reply, but don't forget e.g. Andrew Tanenbaum's Minix - some code was made exactly for educational purpose. (There should be a cone for that: classic co

Obvious reply, but don't forget e.g. Andrew Tanenbaum's Minix - some code was made exactly for educational purpose. (There should be a cone for that: classic codebases for production and classic codebases for education.)