Given that you're asking from a throwaway (and especially given your choice of nickname), you're almost certainly trolling -- but given how old this thread has become, I think it's safe to answer here for the sake of posterity...

OpenStack and SmartDataCenter address some similar problems: they both manage fleets of physical machines and provide orchestration (provisioning, monitoring, etc.) of standing virtual machines on those physical machines. But in every other regard, these two projects are very dissimilar: they differ in their goals, in their organization and in their technology choices.

Getting more specific, I (obviously) have a dog in the fight, so it's hard for me to look at this with an outsider's perspective -- but I think the most nonjudgemental way of phrasing the fundamental difference is that SmartDataCenter is opinionated where OpenStack gives architectural choice to the integrator and/or operator.[1] So in SmartDataCenter you don't pick the storage substrate (it's ZFS) or the hypervisor (it's SmartOS) or the network virtualization (it's Crossbow). While OpenStack deliberately accommodates vendor differentiation, SmartDataCenter deliberately rejects it: we are designed for commodity storage (shared-nothing -- and no RAID controllers, please!), commodity network equipment (no vendor-specific SDN) and (certainly) commodity compute. The upshot is that the integrator/operator needn't design the system themselves -- which we know from experience can result in greatly reduced times of deployment. (Indeed, one of the great prides of SmartDataCenter is our install time: provided you're racked, stacked and cabled, you can get a cloud stood up in a matter of hours rather than days, weeks or longer.)

That fundamental difference -- opinion vs. choice -- has many ramifications. For example, we have no interest in governance (sorry, democrophiles!); if someone has a good idea, we'll do what most open source projects do and let our user community make that determination. This is not to be overly controlling; anyone who disagrees with us (or with anyone!) is welcome to fork the project -- we have deliberately selected a fork-friendly license in MPLv2. We also have no interest (zero, none, nada) in legacy enterprise hardware vendors that are interested in cloud computing only as a vector for preserving their inalienable right to screw their own customers; there won't be "hooks" or "plugins" in SmartDataCenter or generally other such sheep-like wolves.

There are many differences, of course, but I think many can be explained by the fundamental difference in engineering principles of the two projects.

Anyone who is interested in the nature of the opinions asserted in SmartDataCenter -- or in helping form new ones! -- should check out the repos[2][3] (we try to document our thinking), join the mailing lists, and/or join us in IRC at #smartos on Freenode.

[1] This is a bit of a "pro-choice/pro-life" nomenclature in that I have deliberately picked nomenclature that I think these two projects would use to put themselves in the best light. More candidly, I would say that OpenStack seems to me to be a discombobulated mess -- and I'm sure to OpenStack, SmartDataCenter would seem supremely fascist.

[2] https://github.com/joyent/sdc

[3] https://github.com/joyent/manta