The main difference is that the Nanobox PaaS is portable, making it what's been termed a "micro-PaaS". You can host with whatever cloud provider (AWS, DigitalOcean, Linode, Google Cloud) you want or set it up on-premise.

Businesses who want to (or have to for compliance reasons) use a different host (e.g. Vultr in Europe or Alibaba Cloud in Asia) can simply create their own adapters and deploy away: https://docs.nanobox.io/providers/create/

Well, to begin with, Heroku has a bare minimum of interactive functionality, and this is a containered VM with a fancy cPanel successor. How are they similar?