They both support Heroku-like buildpacks. Major difference IMO is that Flynn supports databases and other stateful services. I evaluated Flynn, Deis and Dokku

They both support Heroku-like buildpacks. Major difference IMO is that Flynn supports databases and other stateful services. I evaluated Flynn, Deis and Dokku and wasn't entirely satisfied with any of them opting for Heroku instead. I've promised people a blogpost on this and I will do it once I get time to evaluate RancherOS too.