Anyone actually know where this product would fall in the development pipeline? It sounds amazing.
Edit: Okay, got it, it's a configuration management application which only applies if you're manually handling your AWS containers.
Terraform is a tool that captures Infrastructure as Code. Flynn appears to be a PaaS, akin to something like Heroku with scheduling capabilities on top. Under the hood, there is some sort of infrastructure that Flynn is deploying to; it's providing an API on top of it to easily manage deployments and scaling. Terraform is the tool that defines the layout and composition of underlying infrastructure resources.
Another one of Terraform's strengths is that it supports multiple providers. Most of this thread mentions AWS, but Terraform also supports GCP, Azure, and DigitalOcean. But Terraform can manage anything with an API, so you can codify things like GitHub teams and permissions, DNS configuration, PagerDuty escalation policies, and so much more (https://www.terraform.io/docs/providers/index.html).
All of these definitions are captured in code. You can bring that code under management of source control to get peer review, pull requests, or permission models (signoffs) too.
If you are an individual developer happy with Heroku or Flynn, Terraform probably isn't the best choice for you, especially if you do not have a background in operations or you do not want to manage servers. However, most medium->large scale production applications cannot be supported by such technologies and demand a tool like Terraform to manage the complexity.
I hope that clears up the differences a bit.
Disclaimer: I work for HashiCorp, the company that makes Terraform.
Terraform allows you to manage VPC, network, routing table , firewalls and gateways in the cloud. There is no other software to do that (only manual click in the AWS website).
It can also create AMI, instances and auto scaling groups but there are many tools in that field that do it better.