There are cooperatives (coops), were workers are also owners. But there you are not working for several companies building equity on all. But most US I knew of are no longer active. Only https://www.gcoop.coop/ in Argentina.

Oh, and found this articles: http://www.vintagedigital.net/content/setting-software-co-op and https://www.scribd.com/document/26587085/Tech-Coop-How-To

And also the Hacking Business Model proposed by Monty from MySQL fame was similar to the coop model: https://www.forbes.com/sites/reuvencohen/2012/07/25/the-hack...

(OP) I've actually been trying to figure this out myself and haven't found one yet. Started this Ask HN (https://news.ycombinator.com/item?id=33978686) to try to find out.

My prediction is that we will start to see more over the coming years though. Whether that means finding creative ways to share equity/upside, or using more contractors and part-time folks.