I only know of contentful which looks very similar.
It costs a monthly subscription and doesn't appear to be open source.
Up until the $150 mark there's nothing I see that shouldn't be doable on a standard home desktop machine in a reasonable amount of time.
This would make more sense to me as an outright purchase but that model seems to be out these days.
That's not so easy to support with just a desktop machine.
ps: i work for this
I think this paradigm - a CMS that builds out to static files - is really powerful. The notes about speed and scale are spot-on, nothing is reliably faster than just nginx serving flat files.
I'm working on a microblog system based on the same basic idea.