Illumos

Illumos is a derivative of OS/Net (aka ON), which basically is a Solaris/ https://alternativeto.net/software/OpenSolaris/ kernel with the bulk of the drivers, core libraries, and basic utilities. It is dependent on OS/Net, which Illumos will follow very closely while allowing to retain changes to code which might be unacceptable to upstream https://alternativeto.net/software/OpenSolaris/ . Illumos is aiming at 100% ABI (Application Binary Interface) compatibility with Solaris ON, focusing just on the core foundation blocks.