Installing Valkyrie is as simple as:
$ drush dl valkyrie
N.B. Valkyrie supports both Linux and OSX operating systems. We have no plans to support Windows.
Valkyrie is a Drush extension, and thus requires a recent version of Drush. We currently recommend using Drush 7.x. Earlier versions may work, but are not currently well-tested or supported. Note that Drush can be installed stand- alone, if you are unable or unwilling to upgrade your system install.
Valkyrie depends on Vagrant, which in turn requires Virtualbox. These projects publish their own packages for most operating systems. We recommend installing these, as it will ensure that you are running on recent versions, and thus can take advantage of newer features.
Valkyrie also makes use of some Vagrant plugins: vagrant-triggers, and (for Mac users only) vagrant-dns. Installing these should be as simple as:
$ vagrant plugin install vagrant-triggers
$ vagrant plugin install vagrant-dns # OSX only
Valkyrie also uses git quite extensively. So if you don't already have it installed, go ahead and do that next.