I have actually used the hosted version of Sandstorm in the past with some success, but did not realize at the time that they also offered self-hosting for it.
While I won't get into the specifics of the pros and cons of each of their bullet points, I will say HomelabOS arose (as some of the other commenters have pointed out) as a way for people interested in this sort of thing to experiment with it. Sandstorm looks more geared toward being usable by 'anyone', which is an admirable goal, if perhaps a bit ambitious in my mind.
In general though it looks like they are taking a very different approach to deployments as a whole. They describe some of those differences here: https://sandstorm.io/news/2014-08-19-why-not-run-docker-apps
While I won't get into the specifics of the pros and cons of each of their bullet points, I will say HomelabOS arose (as some of the other commenters have pointed out) as a way for people interested in this sort of thing to experiment with it. Sandstorm looks more geared toward being usable by 'anyone', which is an admirable goal, if perhaps a bit ambitious in my mind.