Puppet and Chef do basically the same things: they let you define how a server should be configured, and the respective applications make changes to the server

Puppet and Chef do basically the same things: they let you define how a server should be configured, and the respective applications make changes to the server so that they converge upon that definition. Fabric is a "library and command-line tool for streamlining the use of SSH for application deployment or systems administration tasks." In other words, it's shell scripting in Python that makes it easy for the author to switch contexts between local and remote commands, or run a series of tasks. It makes no attempt to converge to a known state like Puppet or Chef; it simply runs what you tell it to. Vagrant is a bit different; it connects to VirtualBox or VMware to give you disposable VM for use as a development environment. So, if your application is deployed on Debian configured a certain way, someone on your team can make a Vagrantfile that tells your local computer to fire up a Debian VM and configure it a certain way that is similar to how it is in production. (That configuration might actually be done by Puppet or Chef - Vagrant just builds the VM and fires it off.) It prevents various cross-platform issues from being an issue during development, aka "it works on my machine!" syndrome. Finally, Docker is a way to run a super lightweight container, like a VM, but taking advantage of various Linux kernel capabilities, preventing you from needing the overhead of yet another OS. Your Docker images might have a full VMs worth of content for libraries and such, but they'll not need to actually run as an OS. (Only the libraries needed for your app will be loaded.) With the exception of Puppet and Chef (which are directly competing products), all are very different tools that can be used simultaneously at various parts of the product lifecycle. Does this help clear things up a bit?