OpenSolaris is an operating system kernel.
We're currently evaluating how to boot OpenSolaris via coreboot using the GRUB2 payload.
OpenSolaris has moved to multiboot, so GRUB2 contains all necessary parts, except maybe the filesystem support (ufs compatibility must be checked, zfs doesn't exist yet for grub2).
The instructions on Shudong Zhou's blog don't work anymore, because Sun changed the boot mechanism (again).
what should work (but doesn't for me, yet):
multiboot /platform/i86pc/kernel/unix module /boot/x86.microroot (that filename might be different)
| I, the copyright holder of this work, hereby release it into the public domain. This applies worldwide.
In case this is not legally possible: