Vagrant - Virtualized development for the masses.
Why Vagrant Changes Everything
Vagrant lowers development environment setup time, maximizes dev/prod parity, and makes the "works on my machine" excuse a relic of the past.
Developers no longer need to worry about setting up complicated infrastructure components. Projects with conflicting dependencies can each get their own sandbox -- keeping a developer's workstation free of the hacks needed for multiple versions of software to coexist.
