It's somewhere between Heroku and DigitalOcean. We have a CLI for managing and deploying apps that's very similar to Heroku. But apps also get private networking, disks, load balancing for TCP/UDP.

We do have people deploy single instance apps and use them just like you'd use a Droplet. "fly ssh console" will SSH you directly into them, and with a persistent volume you can do all kinds of fun stuff.

Haven't heard about them, but its more like Heroku - not pure VMs but instead IaaS where you deploy apps using CLI and they manage/scale machines for you.